Nazi Germany (1942)

High Altitude Fighter – Reconnaissance

Approximately 690 Built

Introduction:

The end of the battle of Britain was the beginning of an escalating air war which would claim nearly all of Europe as its theater. While neither air force could be said to claim the Channel in its entirety, low level fighter sweeps, tactical bombing raids, and high level photoreconnisance efforts would be conducted with ever more sophisticated methods and technology over the coming years. High flying recon planes, in particular, would prove the most challenging to combat, as specialized aircraft, like the Ju 86p, began to appear alongside ever faster fighter planes equipped with cameras. With the air war quite literally being taken to new heights, it would take a considerable effort to modify existing fighter planes to enable them to deal with an enemy operating at extreme altitude. In Germany, such efforts would produce the high altitude, ‘odd numbered’ variants of the Bf 109G, which would incorporate nitrous boosting systems and pressurized cockpits to enable them to chase targets far above their unmodified counterparts.

No laughing matter

Prior to the Second World War, high altitude fighter development was a largely secondary issue, in comparison to the build up of aircraft geared for combat at low and medium altitude. The premier fighters of the battle of Britain, the Spitfire Mk I and the Bf 109E, both exemplified this, the latter possessing a single stage, two speed supercharger, and the former a single stage mechanically driven variable speed type. The performance of both aircraft declined considerably as the planes rose above six kilometers. After the battle of Britain, the once highly active theater of Western Europe became secondary to the battles waged in the Mediterranean and the East. The primary activities there soon became focused on intelligence gathering and nuisance raids; there was an escalating nightly strategic air war, however, it was largely dislocated from the efforts of both the RAF’s and Luftwaffe’s daylight forces.

In 1941, both sides would introduce two aircraft which would largely shape the high altitude mission, namely the Ju 86P and the DeHavilland Mosquito. Neither aircraft could be caught by the conventional models of either the Bf 109 or the Spitfire, and thus a race to design high altitude models of the fighters began. For the Germans, the process would be far more complicated, as the reduced supply of certain critical materials meant that the traditional methods of increasing performance were off the table. There was insufficient nickel for corrosion resistant exhaust valves, no tin for heavy duty bearings, and eventually, less cobalt and chromium for heat resistant alloys. On top of this, a transition to synthetic fuels would further complicate matters. While the Battle of Britain-era Bf 109E could boast of both good performance and reliability, its succeeding F model would be plagued by a number of issues, and its increased performance was accompanied with horrible mechanical reliability. In short, nickel poor exhaust valves corroded and failed and the untested C3 synthetic fuel degraded in rubber fuel tanks and escaped into the oil system. Fuel escaping into the oil system was common on most aircraft, but it often happened in small quantities that were subsequently boiled off. The droplets which failed to aerosolize in the DB 601N tended to be of a larger than normal volume, and combined with Daimler Benz engines running cooler than most, they often failed to boil off.

With the new model of Bf 109 in such a sorry state, any new major modification of the engine was forgone, and boosting high altitude performance would fall on some external system. However, the Germans already possessed and employed such a system the year before. GM-1, or Goering Mixture-1, was a nitrous oxide injection system which was used to boost the high altitude performance of a late and uncommon model of the previous aircraft, the Bf 109E-7NZ. The mixture worked as a means of delivering oxygen into the engine’s combustion cycle at altitudes where the supercharger’s boost could not supply the boost pressure to run the engine at emergency power. Additionally, the mixture had the added benefit of cooling the engine when the mixture was injected at a low temperature. Carried in bottles behind the pilot’s seat, the mixture would be pumped into the compressed air circulating in the supercharger, after which it entered the manifold. Even when the supercharger was failing to produce the compression needed, any decrease in the volume of oxygen would be offset by that which was being delivered by GM-1. However, the system was not without its disadvantages. Namely, it increased the weight of the aircraft and provided only a marginal increase in power at low to medium altitudes, where a supercharger had no difficulties in providing sufficient boost to the engine. In short, GM-1 was dead weight below an engine’s full throttle height and, thus, the system had no real place on board a general use fighter plane. Transporting the mixture was also an issue, as GM-1 had to be transported either by pipeline or refrigerated trucks, after which it was transferred to smaller bottles. As it was kept cool, it could not be kept aboard a grounded aircraft and was usually loaded aboard as part of its pre-flight preparations.

Its limitations aside, it was clear that GM-1 was the only means by which the Bf 109 could achieve the much needed high altitude performance.

One Step Forward, Two Steps Back

The trouble with the Bf 109 F’s DB 601N engine would be solved mostly by the introduction of the DB 601E. The new engine switched the fuel source to the lower octane B4, its direct injection pumps were adjusted to prevent fuel drops from entering the oil system, and some of the more fragile components of the engine were redesigned. Prior to this, the Bf 109F ran at a reduced maximum output prior to the Spring of 1942. With the restriction rescinded, it was allowed for the maximum rated manifold pressure to rise from 1.3 ata to 1.42, and it could finally run at its intended, full emergency power.

The new engines were installed aboard the Bf 109F-3 and F-4, and were largely satisfactory, but the delay in achieving their full performance was considerable. The success of the new model DB 601E meant that high altitude developments could continue, and the first new model, after over a year, was the Bf 109F-4/Z. The engine was similar to the early DB 601N aboard the high altitude E-7Z, and delivered roughly the same level of performance, however, the structural and aerodynamic improvements of the F model allowed for better handling and maneuverability. Like the earlier E-7Z series high altitude fighter, there were no standardized provisions for photoreconnisance equipment. The GM-1 system too was improved and expanded on. The tanks were moved from behind the pilot into the wings, which increased the total to 100 kg. The mixture too was stored in a chilled, liquid state which increased its potential horsepower increase from +3 bhp per gram to +4.

It is difficult to ascertain the success these aircraft had, as no distinction was made between F-4 subtypes for kill claims. However, an F-4 of JG 1, a unit which did possess the high altitude variant, brought down a Mosquito at high altitude on August 19, 1942. Lieutenant Gerd Scheiger engaged Mosquito W4065 on a bombing raid to Bremen, at a height of 8.8 km. Given the extreme altitude of the engagement, it is very likely the aforementioned Bf 109 was a high altitude model.

The few Bf 109F-4Zs would serve on every front with considerable success, though access to GM-1 could be problematic across the Mediterranean and on the Eastern Front. However, these troubles were nothing compared to the issues soon to arise with the aircraft’s successor. The Bf 109G series hoped to bring a much desired increase in performance with its DB 605A engine. Effectively developed by boring out the cylinders of the preceding DB 601E, its volume and compression ratios were increased considerably. Along with improvements to its supercharger, and built with a crankshaft able to handle higher RPMs, great hopes were placed on the engine. They were soon shattered. Almost as troublesome as the DB 601N, the engine faced a variety of harsh teething issues. Worst of all were its fragile, corrosion prone exhaust valves and an insufficient oil scavenge system made worse by a switch from ball to sleeve bearings. The series would not reach its potential for almost two years, as Daimler Benz worked through these issues. However, in perhaps the clearest example of the confusing and disjointed relationship between the Luftwaffe and its contractors, they failed to ensure a continuity in materials between the engines in its development branch and those being produced for the Luftwaffe. At an RLM meeting on May 19, 1942, it was revealed that the valves on the test engines had a nickel content of 14%, while those shipped to the Luftwaffe possessed only 8%. This, and similar discrepancies delayed effective testing for some time.

Regardless of the disasters brought on by the lower quality economy alloys, and the misadventures between the Luftwaffe and its contractors, development of the high altitude Bf 109 continued apace.

Under Pressure

The new supercharger on the Bf 109G was extremely promising, and was one of the only things that really worked when the aircraft was introduced. With it, a new high altitude model and standard fighter were produced. The G-1 and 2 were largely built along the same lines as the late F-4 series, with a series of improvements to its armor and instrumentation. The G series also incorporated a series of standardized, modular Rustsatz kits, which could represent anything from bomb racks to photographic equipment. However, these initial models brough little improvement, as they were soon prohibited from running above 1.3 ata in manifold pressure, or in other words, without an emergency power setting. However, the G-1 would prove fairly innovative thanks to a number of new features.

Of the two, the G-1 was the specialized high altitude model, which would include both the ability to carry the GM-1 system, and was equipped with a pressurized cockpit. The cockpit pressurization allowed for a pilot to remain at extremely high altitudes without encountering any of the discomfort one would otherwise experience. Without these aches, pains, and numbness, a pilot was far less likely to become fatigued after long flights at extreme altitudes. The cockpit pressurization system was rudimentary, and was kept pressurized by a compressor which drew from a small scoop left and forward of the pilot. Silica pellets were also installed in the canopy and windscreen to prevent fogging. The GM-1 system too was improved, being made modular and paired with a set of fuselage racks which allowed for the fitting of a reconnaissance camera. GM-1 would also be made available to all subsequent models of the Gustav, regardless of pressurization gear.

The first of these aircraft were built in May of 1942 at the Erla plant and were subsequently handed off for testing and familiarization with Luftwaffe crews. These planes were then used by the 11th staffel of JG 2, noted as their high altitude unit, and began operations on July 17. The unit was first based in St. Pol in the Netherlands and would be assigned to the area before later being redeployed to Germany, and then to the Mediterranean in November, and then transferred to JG 53 before the end of the year. JG 5 also received a number of the planes some weeks after JG 2, the unit being assigned to various bases in Western Europe until the end of the war. Beyond these combat units, the aircraft was operated by the training units Ergänzungs-Jagdgruppe West and JG 105.

In service, the aircraft performed well. In particular, the pressurized canopy was well regarded, and performed well enough to see its inclusion in several succeeding models of the aircraft. Curiously enough, the aircraft were not reserved exclusively for high altitude use and was instead used much like the standard version of the fighter. Their use as high altitude interceptors was more typical of the European squadrons, which had the benefit of better access to GM-1. Even then, G-1’s were still sortied to engage targets at all altitudes. Among the earliest victories came on July 11,1942, when Unterofficier Herbert Biermann engaged and downed a low level Mosquito which had attacked rail traffic near the Danish town of Tonder, after a raid on the U-boat pens in Flensburg. The plane had been damaged during the raid, which undoubtedly helped the pursuing Messerschmitt.

The Up Swing

In spite of the debacle that was getting the DB 605A into service, improvements were slowly being made. Experiments with face hardened, chrome plated exhaust valves would give way to a workable solution to corrosion, and combined with added oil throwers and a new oil centrifuge, would eventually allow the plane to run at its highest power setting. The restrictions would finally be released by August 1943, over a year after the aircraft first entered service.

At the beginning of the year, the Bf 109G-3 had superseded its predecessor. The aircraft’s largest difference, apart from its engine improvements, were its larger tires. Small bulges were added to the top of the wing to accommodate the enlarged landing gear, and the larger tail wheel was now non-retractable, adding a not inconsiderable amount of drag. These changes were made to give the aircraft better ground handling and allow it to better operate out of rough airfields in the Eastern Front and the Mediterranean.

Unlike the previous model, the G-3 saw increasing use against USAAF daylight bombing raids. The raids had started small in late 1942, often against targets nearest England. By the Summer and Autumn of 1943, the raids had escalated continuously and were increasingly focused on targets within Germany. By then, the major focus was on the so called ‘panacea’ targets, which numerous war planners thought could bring an early end to the fighting. Ball bearing and aircraft assembly plants received particular attention.

The bombers of the 8th Air Force often flew at extreme heights, with B-24’s averaging about 22,000 ft, and the lighter loaded B-17 at or above 25,000. Despite being above the altitude where most Luftwaffe fighters could not sustain emergency power, this advantage, and the heavy defensive armament of these bombers, did not translate into a sufficient defense against fighters. While the high altitude Bf 109G-3’s did have the edge, it was largely unnecessary, as the Luftwaffe only made massed attacks against the formations until after the bombers had passed over the Low Countries, where their fighter cover could not follow them. Thereafter, they were harassed by all manner of fighters, from light single-engined types, to night fighters pressed into daylight use.

In the case of the Bf 109, they followed Generalmajor Adolf Galland’s recommendation. The method involved attacking bomber formations at frontal angles in massed attacks using formations no smaller than the four plane schwarm. These attacks were conducted to help cope with the somewhat inadequate armament of the Bf 109, and to reduce the likelihood of being hit by the defensive gunners of the bomber. During a frontal attack, a bomber’s pilots and engines are the most vulnerable, which is quite important considering the single 20 mm aboard the Bf 109 was regarded as inadequate for bringing down a heavy bomber and thus needed to be directed toward these critical areas. Underwing gunpods were somewhat commonly fitted, though their impact on flight performance was considerable. The real breakthrough in anti-bomber weaponry came with the 30 mm Mk 108 autocannon, though its late introduction meant supplies were tight until mid 1944. The frontal attack also ensured the highest possible closure rate with the formation, making the small fighter a much more difficult target for any defensive gunner, and allowed the fighter to strike at the bomber’s engines and cockpit.

Large scale anti-bomber tactics employed early warning radar to track bombers during their ingress into German held airspace, and after they had passed the range limitations of their escorts, the Luftwaffe tracked the formation using trailing Ju 88’s and other long range aircraft. Fighter units would be massed over radio beacons until they received the order to attack and were vectored on to the bomber formations, where they could meet them in numbers. The height of their success was seen in Autumn of 1943, when USAAF planners were hoping to accelerate their progress on Operation Pointblank, seeking to cripple the German aviation industry. On August the 17th, the 8th Air Force prepared for its largest raid yet, with 376 B-17’s dispatched to attack the ball bearing works at Schweinfurt and a Messerschmitt factory at Regensburg. Both of these facilities were located deep within Germany and most of the journey would see the B-17’s outside the area where they could be escorted. To compensate for this, the flight over Regensburg would continue over the Alps and into Allied controlled Tunisia. It was hoped that flight over the Alps would prove easy, and in the case of the Schweinfurt force, they believed that the German fighter squadrons would still be on the ground refueling after their first attacks while the bombers made their return. Both waves would be met with disaster, as the Luftwaffe would hit both forces after their escort fighters turned for home, and the Luftwaffe fighters had taken to the air again as the Schweinfurt raiders made the return trip.

Of the 376 bombers to leave England, 60 would be shot down, 176 were damaged, and 30 remained in North Africa, where they awaited repairs at the overburdened facilities in Tunisia. Losses in combat and written off airframes amounted to 31% of the dispatched force; in contrast, the Germans lost only 28 fighters. In effect, the Luftwaffe was able to effectively deny large portions of their airspace to the raiders. A stalemate in the air ensued in the following months, with new challengers further shifting the balance of power next spring.

Wilde Sau

In addition to the typical daylight squadrons, several Bf 109G-3’s and 5’s were passed on to the single engine night fighter unit JG 300, its sister squadrons 301 and 302, NJG 11, and the first staffel of the 10th Night Combat division. The new G-5 was much the same as the 3, save for its 7.92 mm guns being swapped for 13 mm ones. Originally formed as an experimental unit in the spring of 1943, JG 300 was meant to test the suitability of single engine fighters for night interception use. The initial premise of the unit was to engage RAF bombers over their targets, where the light of the fires and searchlights would make the planes more visible against the ground and cloud cover, and thus enable interception without the use of ground control and onboard radar systems. The squadron saw mixed success and was expanded upon after the bombing of Hamburg, when the RAF succeeded in spoofing the shared frequency of Wurzburg ground based and Fug 202 airborne radar systems with chaff. The Luftwaffe would recover in the span of several weeks, though the attack made the idea of radar-less night fighting alluring.

The group was expanded upon with the 301st and 302nd squadrons being established. While the hope of transitioning daytime fighter squadrons to night use was deemed infeasible due to the amount of training required, the combined unit would continue its task, being joined by a staffel of the 10th Night Combat Division. The task of carrying out the interceptions over raided cities was an exceptionally dangerous one, as they shared the space with flak units, and by the end of the year, enemy night fighters.

There was also a transition away from the unguided wild boar tactics to ground directed interception in order to deal with high flying Mosquito pathfinders and bombers, which no Luftwaffe aircraft could effectively catch until the Me 262B provisional night fighter was introduced. In this role, the single engine night fighter would be directed into a fixed ‘Himmelbett’ intercept zone which covered either the approach, or departure path of the detected enemy aircraft. There, the target would be tracked by the Himmelbett zone’s dedicated radar and searchlight units while the fighter would be guided on to the target. This was an exceptionally difficult task owing to the speed of the Mosquito, and could prove exceptionally dangerous if the aircraft being chased turned out to be a night fighter. As RAF night fighters began to escalate their intruder missions, transiting to and from interception areas became much more dangerous. While the Mosquito night fighters were larger and less nimble than the Bf 109, their radar systems allowed them to catch the otherwise “blind” daylight fighter.

The success of these units was mixed, though some extraordinarily capable pilots achieved some very impressive results. The best of them was Lt. Kurt Welter, who by the end of the war was in command of the only night fighter unit equipped with Me 262’s. On the night of August 30th, 1944, Lt. Welter flew a Bf 109 which had been vectored over the Stettin raid area. In the span of ten minutes, he attacked four Lancaster heavy bombers, two of which were later confirmed destroyed, these being 115 Squadron’s PB131 and 12 Squadrons’s PD 273, representing his 14 and 15th confirmed victories. Most pilots, however, achieved considerably less success owing to the extremely high level of flying and combat proficiency their missions demanded. Mosquito interception duties were the most difficult owing to the speed and altitude of the light bomber, which could often exceed 8 km. To aid these pilots, a number of rare Bf 109G-5’s with high altitude DB-605 AS engines were made available to these squadrons. Nonetheless, Mosquito interception remained a gamble depending on the distance at which the bomber was detected, whether a fighter could be launched fast enough to climb, and still have enough time to be vectored into its flight path.

Crowded Skies

By the end of 1943, the newest and last iteration of the high altitude series was in service. The new Bf 109G-5 now carried a pair of 13 mm MG 131’s in the place of its 7.92 mm MG 17s, this increase being installed after long standing complaints regarding the inadequacy of the machine guns in the upper cowling of the plane. The heavier guns and the enlarged cowling meant the aircraft was slower than the one it replaced. This proved fairly concerning, as no major improvements in engine output were expected for the foreseeable future. These aircraft were distributed to units on all fronts and used much like their standard, non-pressurized counterparts. Most were deployed in the strategic air defense of Germany, where they soon faced a new, and very dangerous opponent.

The P-51B Mustang appeared to be the solution to bomber offensive’s ills, being a fast, maneuverable fighter with incredible range and high altitude performance. The danger of this new threat was quickly recognized by one Generalmajor Joseph Schmidtt, who began to advocate for the need for GM-1 equipped Bf 109s to act as top cover for the previously secure massed fighter formations. In this, the aircraft proved a mostly adequate stop gap, performing much better than other models, but it still lagged behind the American P-51B and the P-47D at altitude. In short, the Bf 109 was an old airframe, operating with an engine which had become fairly outdated after significant delays in getting it to reach its highest power ratings. Even worse, many of the airframe’s changes over the years had negatively impacted its performance, especially the addition of the non-retractable tail wheel, and the enlarged upper cowling to accommodate the larger machineguns.

However, there were still some areas of improvement. In particular, the supercharger was swapped for an enlarged version which came from the DB 603 engine. Switching the engine entirely was completely unfeasible. The Luftwaffe’s research and development could be chaotic at the best of times, and 1944 certainly was not the ideal environment for such a big risk. The bombing raids too were making their mark as, while they had failed to curtail the German aviation industry entirely, they had forced a consolidation of existing designs. In effect, German bomber production plummeted in order to bolster production of a series of fighter designs which saw very slow modification rates. The vastly expanded use of slave labor in the following months also created no shortage of trouble, with quality slipping sharply as skilled workers were increasingly drafted into the Wehrmacht, and slaves increasingly sabotaged components.

The final models of the G-5 used the DB 605AS engine, with the much larger supercharger designed to improve high altitude performance. The effort was largely successful, though only a few Bf 109G-5’s would ever be equipped with the engine. As much as pilots enjoyed the comfort of the pressurized canopy, it was an expense that Messerschmitt and their directors at the Jagerstab were no longer willing to accept. The G-5 would be the last model to carry it. The Luftwaffe’s fortunes too declined sharply, as P-51 fighter sweeps periodically attacked airfields once considered safe, and the brutal war of attrition had eroded the number of remaining experienced pilots further. Attacks on Germany’s synthetic fuel production in the summer of 1944 introduced a final, and catastrophic crisis which largely left the Luftwaffe crippled for the remainder of the war.

G-5 production was phased out entirely in June of 1944, as Messerschmitt moved to consolidate Bf 109 production with the G-14. The supply chain would however remain disjointed, as they produced models using the standard DB605A, and the high altitude DB605AS. The G-14, with its standardized, low altitude MW50 boost system, did help reduce the performance disparity at low altitudes, with the aircraft possessing an excellent rate of climb and acceleration, but high altitude performance equivalent to the best Allied fighters would elude the Bf 109 for the rest of the war.

Handling and Flight Characteristics

The Gustav, as with nearly all Bf 109 models, was maneuverable, but its increased weight had made it somewhat more cumbersome than its predecessors. Initially developed to be as light as possible while carrying with it a powerful engine, the continued added weight with a comparatively little increase in horsepower resulted in control harmony compared to earlier models. Test pilots noted that while aileron and rudder forces were light, while the elevator was fairly heavy, an issue which was exacerbated at high speed. While the aircraft was exceptionally nimble at low speeds, which was well aided by the wing’s leading edge slats, heavy rudder forces and stiff elevator controls severely impacted handling at high speed. At lower altitudes, the rudder forces became excessive at around 500km/h IAS, at higher altitudes, upwards of 7 km, the controls remained lighter at higher speeds and permitted better control. Dive performance was respectable, though given that the controls were nearly seized in a high speed dive, it could prove very dangerous at lower altitudes. Maximum level speed was decidedly mediocre, though the aircraft boasted a high climb rate and good acceleration thanks to its high thrust to weight ratio.The plane was otherwise stable and, by most accounts, with good level flight performance.

The cockpit was both cramped and provided exceptionally poor visibility. The deep set seat, with its heavy cockpit framing, greatly restricted the pilot’s view, especially towards the forward and rear aspects. A few late production Bf 109G-5s were equipped with the improved Erla canopy, as became standard on late war 109’s, and provided much better visibility to the sides and rear of the aircraft. The cockpit was among the smallest on any fighter during the time period. Pilots often felt it claustrophobic, which is understandable considering the centerline cannon for the aircraft rested between the pilot’s shins.

Operation of the Gustav was extremely straightforward, given the high level of automation the DB 605A possessed. The engine was controlled through a series of linkages between components which adjusted one another as the pilot adjusted the throttle lever. The supercharger, radiator, propeller RPM, and mixture were all managed automatically, though manual control was also possible. The core of these linkages was the propeller RPM, which was preset to an accompanying manifold pressure. The rest of the engine largely adjusted itself around this setting. In stark contrast to this truly modern feature, the plane still had manually operated flaps, which were retained through the end of the war. The aircraft lacked traditional trim tabs. Instead, the aircraft’s trim was set on the ground to match its cruise speed. The pilot could however correct for pitch by adjusting the angle of the horizontal stabilizer. Flying the aircraft was otherwise very convenient.

The takeoff run was fairly simple and the aircraft could easily be corrected for the torque produced by the engine. Visibility was poor on the initial run up, but given the relatively controllable nature of the aircraft, it was something pilots easily adjusted to. The same cannot be said of late war versions of the 109, which possessed engine outputs upwards of +1800 PS. Landings under ideal conditions were notably very easy, though were much more difficult in poor weather or when operating from hastily constructed frontline airfields. There was some improvement after the G-1, when the tire tread was increased, but landings and ground handling required a pilot to ensure solid directional control, as the narrow landing gear base could cause trouble.

Comparison with other single engine high altitude fighters, up to the Summer of 1944

Aircraft	Speed at Sea level (km/h)	Maximum speed at critical altitude, unboosted (km/h)	Speed at 10 km (km/h)	Maximum Output (hp)
Bf 109G-1 -Mid 1942-	506	630 at 6.6 km	640 (with GM-1)	1213
Bf 109G-5 -Late 1943-	510	620 at 6.5 km	635 (with GM-1)	1454
Bf 109G-6AS -Early 1944-	506	653 at 8.3 km	630	1415
Bf 109G-5AS w/GM-1 (estimated) -Mid 1944-	“	“	660*	1415
MiG-3 (AM 35) -Early 1941-	472	621 at 7.8 km	<550	1350
Spitfire HF Mk IX -Late 1943-	529	668 at 8.5 km	651	1710
Spitfire Mk XIV -End of 1943-	583	717 at 7.6 km	706	2050
P 47D-10 -Late 1943-	535	700 at 9.4 km	692	2300
P-51B-15 w/wing pylons -Early 1944-	586	685 at 7.2 km	667	1720

*It should be noted that the Spitfire Mk XIV saw service in low numbers, and was a very rare sight until almost a year after its introduction at the end of 1943. The rest of these planes were otherwise quite common.

Along with the Bf 109E-7Z, Mikoyan Gurevich’s MiG-3 debuted as one of the earliest high altitude fighters of the Second World War. The MiG-3’s AM-35A engine had high compression ratios and possessed a single speed supercharger which had been geared for high altitude performance. This allowed the aircraft to achieve a respectable level of performance above 7 km. It did, however, come at the steep cost of having mediocre low altitude performance, and above 8 km, its top speed fell dramatically. The aircraft also earned a reputation of being challenging to fly, a chief issue being its minimum landing speed, which was considerably higher than other Soviet fighters. Due to the lack of action at high altitudes over the Eastern Front, the aircraft was subsequently re-equipped with the AM-38 engine, for low altitude use. Production ceased early in the war, and its assembly lines were turned over to produce IL-2s.

The British followed the Germans in developing high altitude fighters with specialized boost systems. They would go on to produce a series of pressurized, liquid oxygen boosted Spitfires, operating on a very similar set of principles as the GM-1 boosted 109s. These however, did not see as widespread a use, as they were not quite as versatile or reliable, though this is not to say they were unimpressive. The Spitfire Mk VII with a Merlin 71 and LO could reach a speed of 618 km/h at an altitude of 12 kilometers. However, owing to a lack of available information, it will not be discussed in depth here.

A more versatile high altitude Spitfire also existed in the form of the HF Mk IX, which was powered by the Rolls Royce Merlin 71. This aircraft featured an intercooled engine with a two stage two speed supercharger, which provided it phenomenal high altitude performance, along with its broad elliptical wings. The addition of the second stage allows for further compression once the first stage alone reached its limit, and the use of the intercooler increases the upper limit of compression by reducing the temperature of the air entering the manifold. This allowed the engine to be run at a higher boost and was able to maintain combat power at altitudes far higher than the previous single stage 40 and 50 series Merlin engines. In comparison to the Bf 109, the engine can be could at combat power at high altitudes without needing to worry about depleting the supply of nitrous, which at most could last 22 minutes. In comparison, the Bf 109’s DB 605A, which operated using a variable speed supercharger which, while less powerful than the intercooled two stage type, lacked the performance gaps that came with the fixed gearing of the Merlin’s supercharger. In the case of the GM-1 powered series, however, there would have been a similar gap between roughly 7 and 8 km, between the aircraft’s critical altitude and the minimum height for GM-1 use. The use of GM-1 on the later DB 605AS powered Bf 109’s would have likely allowed them to exceed these high altitude Spitfires in respect to linear speed at extreme altitude. The performance figures for the Spitfire Mk XIV, equipped with the significantly more powerful Rolls Royce Griffon, speak for themselves.

The P-47 series of fighters achieved their tremendous high altitude performance through a different method entirely, turbocharging. Much of the interior space below and aft of the cockpit was taken up by a turbo supercharging system which managed to prevent any significant loss in horsepower up to 25,000 ft. The exhaust driven turbine proved a phenomenal means of attaining high altitude performance. Like the variable speed supercharger on the DB605A, the turbo-supercharger was not dependent on mechanically geared stages and thus lacked the associated performance gaps. However, a clear drawback to the system was its complexity, as in addition to the throttle and RPM levers, there was also a turbine lever. While it was possible to link the supercharger and throttle levers together on all but the early models, this was advisable only at certain altitudes. Running the turbine at higher speeds than necessary resulted in some horsepower loss. Regardless of this, many US pilots considered the P-47 far and away the best fighter above 30,000 ft. At high altitudes, where drag was minimal, and with over 2000 hp driving it, the P-47 possessed a speed and maneuverability far greater than its size might suggest possible. Further refinements to the design saw the aircraft exceed 720 km/h above 32,000 ft (~10 km).

The P-51B was driven by largely the same engine as the Spitfire Mk IX and it was eventually geared with usage at medium altitude in mind. In addition to its powerful Packard Merlin, which gave good high altitude performance, what set the P-51 above most was its extremely low drag airframe and wings. Having been designed later than most of the aircraft discussed here, it had the benefit of being able to incorporate the most recent breakthroughs in aerodynamics. Most notably, the use of laminar flow theories in its wing design, its drag eliminating radiator scoop, and its superbly streamlined fuselage, made it among the most exceptional fighters of the Second World War. Its high speed maneuverability too was largely unparalleled, as the laminar flow wing gave it an exceptionally high critical mach number, and its internally sealed control surfaces ensured effective control at very high speed. While its Packard V-1650-7 engine was geared for medium altitude use, it still outpaced both the standard high altitude models of the Bf 109 and Merlin powered Spitfire. When run on 150 octane fuel, as was more or less standard by mid-summer 1944, its performance largely matched that of the Spitfire Mk XIV, though the Griffon engine gave the Spitfire an incredible edge above 30,000 ft. Only the Bf 109G’s equipped with the DB 605AM high altitude engine could give comparable high altitude performance with the Mustang. They could both keep pace with one another above around 9km, though few of the pressurized high altitude model were built.

Production

Production of the Bf 109G began with centralizing supply chains around the Messerschmitt factory in Regensburg, and the subcontracted Erla machine factory. The escalating bombing campaign in 1943 forced a dispersion of the industry, and many components were built at dispersal sites before final assembly took place at either the Regensburg plant, the one at Erla, and later, the Wiener Neustadt aircraft factory. The Bf 109 was fairly well suited to this scheme, but nowhere near as suited as the Fw 190, which made use of much more convenient sub-assemblies. By the start of 1944, the Jagerstab was established to boost fighter production further, in order to compensate for potential losses incurred by bombing raids. They were very successful in this regard; production surged, and the average construction time of a Bf 109G declined from around 5000 hours to approximately 2500. The cost, however ,was substantial. Bomber production was cut to the bone, fighter designs were frozen over long periods, and the long standing use of slave labor skyrocketed. Bf 109G production became more complex as the war went on and the number of subtypes expanded. These would grow to G-1 through 6 and a separate high altitude series of Bf 109G-5/G6-AS aircraft. There was some consolidation between the disparate models with the G-14, though the still separate standard and high altitude models continued to complicate production and supply chains.

Messerschmitt was among the first to mass implement slave labor in late 1942, when they requested and received 2,299 inmates who were forced to work at the aircraft plant at Augsburg. They subsequently requested the construction of co-location camps for the rest of their factories. This marked a transition from skilled paid workers, who were of a dwindling number due to conscription, to a largely unskilled base of prisoners who sought opportunities for sabotage. Brutal retaliation from the SS, who managed security, and a severely declining standard of living saw rates of sabotage climb heavily as the war went on. By the Autumn of mid 1944, it was fairly common to see aircraft losses attributed specifically to sabotaged components. Other unsafe corner cutting practices became more common as well, and even saw the re-use of components scavenged from downed aircraft.

Bf 109G-1 Production

Werknummer	Factory	Period
10299-10318 (20)	Erla	May to June 1942
14004-14150 (147)	Regensburg	February to June 1942

Bf 109G-3 Production

Werknummer	Factory	Period
16251-16300 (50)	Regensburg	January to February 1943

Bf109G-5 Production

Werknummer	Factory	Period
15200-16000 ( with G-6)	WNF	March to August 1943
26000-26400 (mixed with G-6)	Erla	August to September 1943
27000-27200 (mixed with G-6)	Erla	September to October 1943
110001-110576 (dedicated production)	Erla	November 1943 to June 1944
	*a total of 475 G-5s were built, at least 16 converted to G-5AS/R2 recon planes at the Erla plant in Antwerp

Construction

Much like its predecessors, the Bf 109G was a fairly conventional late 1930s fighter design, which sought to install the most powerful engine in a small, lightweight airframe.  At its fore was the engine section, mounted on a steel mount with rubber vibration isolation. The engine oil cooler was mounted to the lower engine cowling, in order to give better access to the Bosch PZ 12 fuel injectors, with the section otherwise containing all of the motor associated systems save for the coolant radiators and GM-1 boost system. Above the engine and on the port side was the compressor scoop for the cockpit pressure system, where it remained until the Bf 109G-5, whereafter it was moved to the starboard side and slightly ahead of the MG 131 fairing. The system consisted of the compressor equipped with a relief valve, an air filter, a three way cock, a pressurizing valve, a negative pressure relief valve, a compensating valve, a pressure line, and removable silica gel cartridges. These components were distributed around the engine and canopy. The system proved fairly robust and was a much welcomed addition to the aircraft. The rest of the fuselage followed a largely conventional semi-monocoque construction, aside from the landing gear, which was mounted to the fuselage and swung inward when deployed. On the G-3, the tires were increased by a width of roughly a centimeter, such that they possessed a tread of 16 cm and a diameter of 66 cm. The associated bumps on the wing tops are the only external feature that allow differentiation between it and G-1. The control surfaces at the rear of the fuselage were operated through a standard cable linkage and were fabric skinned. The incidence of the horizontal stabilizer was adjustable in flight to set the pitch of the aircraft.

The cockpit was seated deep within the fuselage, in order to reduce the frontal windscreen area, though this choice drastically decreased the pilot’s visibility. The thick canopy framing made this issue worse, especially on the pressurized aircraft, which possessed reinforced beams and a non-removable armored seatback formed the rear of the pressurized canopy hood. The cockpit itself was noted as quite cramped by virtually all who flew it, offering little in the way of headspace and shoulder room, and made all the more claustrophobic by the lack of adjustable rudder pedals. At the front of the canopy was an integral 60 mm armor glass windscreen. As with the rest of the canopy frame, it contained silica to prevent condensation at low altitudes, which could then cause icing higher up. Several Bf 109G-5AS aircraft received higher visibility Erla canopies, though they lost their pressurized features. The layout of the instrumentation was clean if dense, though the pilot was aided by a high level of automation, which meant he could largely fly the plane through just the throttle lever. Raising or lowering the flaps and adjusting the stabilizer was done manually through a pair of wheels at the pilot’s left.

The plane’s elliptical wings were attached to the fuselage through a main, centerline bracket and possessed only a single mid wing spar. Connections for the hydraulic lines, which drove the flaps and landing gear, and radiator coolant lines, connected automatically when the wings were bolted to the fuselage. Each wing possessed a radiator located inboard, with airflow controlled by two outlet covers at the rear of the radiator matrix. These covers moved along with the outboard section of flaps when the plane was adjusted for takeoff and landing. The outermost rear section contained the fabric skinned ailerons. The leading edge of the wing had a slat which would extend during hard maneuvers and improve the turning abilities of the aircraft. These could prove troublesome on earlier models in regards to unwarranted deployment and jamming in place, but had been worked out by the G model.

The GM-1 system consisted of the nitrous bottles, compressed air, and the control system. On the Bf 109G, the system existed as part of a Rustzustand or Umbausatz kit which could be installed at a Luftwaffe field workshop or maintenance center, in the latter’s case. The pressurized models shared this with the standardized models, however, they differed in that the glass-wool insulated nitrous bottles were installed in the port wing, instead of in the fuselage, behind the pilot. Later models could have the tanks stored in either position. The GM-1 was kept in a chilled liquid state, which was found to provide a higher boost effect, providing +4 bhp per second per gram over the gaseous +3 bhp. The total volume of the bottles was 115 L, not counting the compressed air which was used to force the mixture through the system. The chilled nature of the nitrous did, however, bring a drawback in that it was released as it warmed and evaporated. An aircraft would need to have its tanks filled immediately before take off in order to have the longest duration. The boost could be maintained up to 22 minutes if the tanks were filled immediately before flight, falling to 19 minutes in the winter and 16 in the summer if the aircraft departed twelve hours later. In the summer, all of the GM-1 could be expended if the aircraft was left parked for two days. The weight of the entire system was considerable, at roughly 100 kg.

Use of GM-1 on the DB605A was prohibited below 8 km, where it provided little benefit, and below which the system was mostly dead weight. With the larger supercharger on the DB 605 AS, this height increased to 10 km. In the cockpit, the pilot possessed a pressure gauge and an on and off switch to control the system. Once activated, it took up to five minutes to have the greatest effect, whereafter the pilot could turn the system on or off as they pleased. At the initial activation height, the mixture could boost the top speed of an equipped Bf 109 by approximately 30 km/h and recover as much as 300 PS at high altitude.

The Bf 109G-3 through G-5 carried either the DB 605A or high altitude DB 605AS, both being an inverted, 35.7 liter, V-12. The reason for it being inverted was to ensure the propeller shaft was as low as possible. This would enable the low mounted, centerline cannon to fire through the eye of the engine without its recoil seriously jeopardizing the aircraft’s stability. This was achieved through the use of direct fuel injection, which was fairly common practice in German aviation by the start of the war, though rare elsewhere. The engine also possessed a high level of automation, which let the pilot manage the engine and most of its associated systems just through the throttle lever. These were essentially a series of linkages between components that adjusted one another as the pilot increased or decreased engine power. It did not possess a true engine control unit, as was used in the BMW 801. Additionally, the engine used a single stage, variable speed, centrifugal supercharger which was mechanically driven by the engine and used a hydraulic coupling for variable transmission. The fluid coupling supercharger automatically adjusted itself via barometric control and was easily the most impressive feature of the engine, allowing it to smoothly adjust its boost as it climbed or descended. This allowed the aircraft to avoid the performance gaps otherwise encountered with engines using fixed speed settings. The engine used B4, which was originally 87 octane, as most of the C3 high performance stocks were dedicated to squadrons flying Fw 190s.

In spite of these innovative features, the engine’s performance was fairly modest for its day. It produced up to 1475 PS, though this was only possible after several major modifications which saw the replacement of the original exhaust valves for chrome plated sets, among other major modifications. The system also had its oil system improved through the use of additional oil throwers to improve flow, and an oil centrifuge to address issues with foaming. Between 1942 and late ‘43, the high power settings on almost all of these engines were disabled in order to keep failure rates manageable. The supercharger too would eventually lag behind its contemporaries, as despite its smoothness, its volume became a bottleneck. This was most apparent in any comparison to the two-stage, intercooled models of the Merlin engine. Some later models would mount an enlarged supercharger with 30% greater volume, derived from the larger DB 603. Nearly all would be equipped with an anti-knock boost system in the form of MW50 by the summer of 1944, which would boost output up to 1800 PS, though the corrosive mixture of methanol and water decreased the engine’s lifespan. Engines with the larger supercharger were designated DB 605AS, those with the boost system 605M, and those with both were 605ASMs. Several Bf 109G-5’s were fitted with the high altitude engine, though none received the low altitude boost system, for obvious reasons.

The engine measured 101.1 × 71.9 × 174 cm, had a bore and stroke of 154 mm (6.1 in.) x 160 mm (6.3 in.), and weighed 745 kg (1,642 lb). Two coolant header tanks were set to either side of the engine, while the oil tank was placed at the front. Compression ratios were 7.5/7.3:1 (left and right blocks) with B4 aviation gasoline, ratios were different using C3 fuel, though this was not used aboard this series of fighters.

Early models were equipped with a pair of MG17 7.92 mm machine guns and a single, centerline MG151/20 autocannon. On the G-5, the MG17s were swapped for 13 mm MG131 heavy machine guns, which both provided a heavier armor piercing bullet, and a round with a small explosive core. While the standard G-6 could carry a centerline 30 mm autocannon, the modification was not available for any of the high altitude fighters. This was likely due to the necessary changes in the canopy required for mounting the larger weapon, which may have been incompatible with the pressurized model. As a firing platform, the 109G was excellent, especially in that all its weapons were placed at the center of the aircraft and thus required minimal adjustments for weapon convergence. However, the aircraft was very lightly armed, especially on the MG17 equipped models. Many pilots considered the armament inadequate, and the addition of supplementary underwing guns severely hampered the aircraft’s performance. These sentiments went as high as the General of Fighters, Lt. General Adolf Galland.

Conclusion

The pressurized models of the Bf 109G proved to be an expedient means of boosting the performance of high altitude squadrons. The pressurized canopy, while later seen as an expensive luxury, was well appreciated by pilots who often flew at great heights on interception and photorecononniance missions. As with their standard counterparts, the series was handicapped considerably by the limitations and troublesome DB 605A. While the aircraft offered good performance for 1943, without any substantive increase in power, the pressurized Gustav series fighters began to lag considerably behind their Allied opponents the following year.

Bf 109G-1 configuration (shared with G-2)	Modification type	Specification
Bf 109G-1/R 1	Rüstsatz	Mid fuselage bomb rack. ETC 500 or Schloss 503 A-1.
Bf 109G-1/R 2	Rüstsatz	ETC 50 rack for four SC 50 bombs
Bf 109G-1/R 3	Rüstsatz	300 liter centerline drop tank
Bf 109G-1/R 4	Rüstsatz	SD-2 cluster munition dispenser rack, 24 SD-2 submunitions
Bf 109G-1/R 6	Rüstsatz	Two underwing MG 151/20 cannons
Bf 109G-1/R2	Rüstzustand	GM-1 high altitude boost system, fuselage racks for camera fitting

Bf 109G-3 Configuration (shared with G-4)	Modification type	Specification
Bf 109G-3/R 1	Rüstsatz	Mid fuselage bomb rack. ETC 500 or Schloss 503 A-1.
Bf 109G-3/R 2	Rüstsatz	ETC 50 rack for four SC 50 bombs
Bf 109G-3/R 3	Rüstsatz	300 liter centerline drop tank
Bf 109G-3/R 6	Rüstsatz	Two underwing MG 151/20 cannons
Bf 109G-3/R1	Rüstzustand	Two wing mounts for 300 liter drop tanks and an ETC 500 rack
Bf 109G-3/R2	Rüstzustand	GM 1 high altitude boost system, fuselage racks for camera fitting
Bf 109G-3/R3	Rüstzustand	Reconnaissance aircraft conversion: Two drop tank pylons, machine guns removed, fuselage camera being either Rb 75/30 or Rb 50/30.
Bf 109G-3/U2	Umbausatz	Alternate GM-1 fitting, no camera provisions

Bf 109G-5 configuration (shared with G-6)	Modification type	Specification
Bf 109G-5/R 1	Rüstsatz	Mid fuselage bomb rack. ETC 500 or Schloss 503 A-1.
Bf 109G-5/R 2	Rüstsatz	ETC 50 rack for four SC 50 bombs
Bf 109G-5/R 3	Rüstsatz	300 liter centerline drop tank
Bf 109G-5/R 4	Rüstsatz	SD-2 cluster munition dispenser rack, 24 SD-2 submunitions
Bf 109G-5/R 6	Rüstsatz	Two underwing MG 151/20 cannons
Bf 109G-5/R 7	Rüstsatz	PR 16 radio direction finding gear, designation not usually applied
Bf 109G-5/U2	Umbausatz	GM-1 boost system
Bf 109G-5/R2	Rüstzustand	Rb 50/30 camera fitted

*Rüstsatz kits are removable on a mission basis, Rüstzustand are installed at workshops, Umbausatz are kits that are built into an aircraft at the factory or a maintenance and recovery center.

Aircraft with FuG 16y radio sets, for command aircraft, received a -y suffix. For example, Bf 109G-5y/U2/R 3 would be a fighter equipped with a radio set for ground control, GM-1, and an external fuel rack.

Bf 109G-1	Specification
Engine	DB 605A
Output	1475 PS
Gross Weight	3050 kg
empty weight	–
Combat Range (internal fuel only)	668 km
Maximum speed (prior to downrating)	660 km/h at 7 km
Armament	2x 7.92 mm MG 17, 1x 20 mm MG 151/20
Crew	Pilot
Length m	8.84
Height (without propeller) m	2.6
Wingspan m	9.924
Wing Area m2	21.6

Bf 109G-5	Specification
Engine	DB 605A, DB 605 AS
Output (DB 605 AS)	1475 PS (1415 PS)
Gross Weight	3350 kg
Empty weight	2543 kg
Combat Range (internal fuel only)	625 km
Maximum speed (DB 605 AS)	630 km/h at 6.5 km (650 km/h at 8.5 km)
Armament	2x 13 mm MG 131, 1x 20 mm MG 151/20
Crew	Pilot
Length m	8.84
Height (without propeller) m	2.6
Wingspan m	9.924
Wing Area m2	21.6

Plane	In use with
Bf 109G-1	I/JG2, 11./JG2, 11./JG26, II./JG51, JG 53,
Bf 109G-3	11./JG 2, 11./JG26, I./JG1 (later II./JG11)
Bf 109G-5	III./JG 1, II./JG 2, I.& II./JG3, II./JG11, III./JG 26, II./JG27, I./JG300, I.&II./JG302, II./JG 11, II.&III./EJG 1, NAG 2, NAG 12, NAG 13, (F)/123

Credits

• Article written by Henry H.
• Edited by  Henry H. and Stan L.
• Ported by Henry H.
• Illustrated by Hansclaw

Illustration:

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