In World War II, Schräge Musik was the name the Germans gave to upward-firing autocannons that the Luftwaffe mounted in night fighter aircraft. A very similar fitment was also used by both the Imperial Japanese Army Air Service and Imperial Japanese Navy Air Service and known by a different, undocumented name in their twin-engined night fighters. The Luftwaffe and the IJN's air arm had their first victories with fighter-mounted upward-firing autocannons in May 1943.
The night fighters used this innovation to approach and attack Allied bombers from below—outside the bomber crew's usual field of view. Few bombers of that era (except for American heavy bombers with ventral (underside-mounted) ball turrets) carried defensive guns in the ventral position. The ventral turret on some early Avro Lancasters was sighted by periscope from within the fuselage, as with the first examples of the B-17E Flying Fortress's remotely operated Bendix-designed ventral turret (before the Sperry ball turret was adopted), and proved of little use. An attack by a Schräge Musik-equipped fighter was typically a complete surprise to the bomber crew, who only realized a fighter was close by when they came under fire. Particularly in the initial stage of operational use, until early 1944, Allied crews often attributed sudden fire from below to ground fire rather than a fighter.
World War I
During World War I, forward firing Lewis guns were frequently mounted on a Foster mounting on the top wing of a biplane. This was so they fired over the revolving propeller, due to the difficulty of synchronizing this type of weapon to fire through the propeller arc. Since the gun had to tilt back to change ammunition drums, it could also fire upwards at an angle. The guns of the Nieuport 11 and Nieuport 17 fighters, especially in British service, and the Royal Aircraft Factory S.E.5a were often used this way, to attack enemy bomber or reconnaissance aircraft from the "blind spot" below the tail. The British ace Albert Ball, in particular, was a great exponent of this technique and developed the tactic of getting under and just behind his adversary, and with his upper-wing mounted machine gun in his SE.5, pulled down on its ratchet tracks at an angle of 45°, was able to shoot down the enemy from below. Ball also mounted another machine gun in the bottom of the cockpit to fire downward. Along with many other RFC and French combat aircraft, the Nieuport 17 used a unique arrangement of Le Prieur rockets mounted obliquely to the interplane struts, and designed for "stand off" balloon attacks.
The concept of off-set or oblique mounted weaponry in night fighting was first used by Royal Aircraft Factory B.E.2c night fighters to attack airships from below. RFC/RAF specialized "Comic" Home Defence night fighter variants of the Sopwith 1½ Strutter and Sopwith Camels of No. 151 Squadron RAF in 1918 were produced to combat the German bomber and airship raids over Great Britain. The armament was two Lewis guns mounted on twin Foster mountings, in preference to the synchronized Vickers preferred for day fighting. They were located at the upper center-section or fixed to fire upwards in a position that prevented the pilot from losing night vision from the flash of the firing guns.
The Sopwith Dolphin, a "multi-gun" fighter design entered service near the end of World War I, armed with two forward-firing Vickers machine guns in the usual location, just forward of the cockpit. However, it could also carry a pair of Lewis machine guns on the forward cross-tube that comprised part of the cabane strut structure—intended to aim forwards and upwards as an anti-Zeppelin armament scheme. They came that way, directly from the factories that produced them. The Germans tried similar arrangements in 1917, when Gerhard Fieseler of Jasta 38 attached two machine guns to an Albatros D.V, pointing upwards and forwards.
The most convoluted example of a night fighter designed to fight at high altitudes was the abortive Supermarine/Pemberton-Billing P.B.31E Nighthawk, the first project of the Supermarine Aviation Works Ltd. The prototype anti-Zeppelin fighter had a crew of three to five and an intended endurance of 9–18 hours. For armament, the Nighthawk had a 1½-pounder (37 mm) recoilless Davis gun mounted above the top wing with 20 shells that had a wide arc of fire, including upward—and two .303 in (7.7 mm) Lewis guns. A trainable searchlight was nose-mounted. First flown in February 1917, the lumbering fighter could only manage 60 mph (97 km/h) at 6,500 ft (1,981 m) and took an hour to climb to 10,000 ft (3,048 m), which was totally inadequate for intercepting Zeppelins. The project was summarily dropped.
The Boulton Paul Bittern was a twin-engined night fighter (designed to Specification 27/24) with a planned armament configuration of barbette mounted guns that could be angled upwards for attack against bombers without having to enter a climb. The first of two Bittern prototypes flew in 1927, though performance was poor and the development stopped.
The Westland C.O.W. Gun Fighter (1930) and Vickers Type 161 (1931) were designed in response to Air Ministry specification F.29/27. This called for an interceptor fighter operating as a stable gun platform for the Coventry Ordnance Works 37 mm autocannon produced by the Coventry Ordnance Works (COW). The COW gun had been developed in 1918 for use in aircraft and had been trialled on the Airco DH.4. The cannon fired 23 oz (0.65 kg) shells and was to be mounted at 45 deg or more above the horizontal. The tactic was to fly below the target bomber or airship, firing upwards into it. Gun firing trials with both types went well, with no detriment to airframe or performance, although the Westland prototype displayed "alarming" handling characteristics. Neither the Type 161 nor its competitor, the Westland C.O.W. Gun Fighter were ordered, and no more was heard of this use of the aerial COW gun.[N 2]
The Boulton Paul Defiant and the naval Blackburn Roc were two late-1930s British fighter aircraft that carried their armament in turrets. This gave them a wide range of fire, including upwards. The fire of several fighters could be brought to bear on a target together. The RAF put the Defiant into service in 1939, intending to use it against bombers, despite the bombers' numerous gun positions. After becoming outclassed as a day fighter, the Defiant moved to the night fighter role, where it had some success, typically attacking from below and slightly ahead of the target bomber, and well out of its field of defensive fire.
In the United States, the twin-engine Bell YFM-1 Airacuda was designed as a bomber-destroyer, touted as, "...a mobile anti-aircraft platform." Its armament included mainly forward-firing M4 37mm cannon, with an accompanying gunner mounted in a forward compartment of each of the two engine nacelles. Theoretically, the cannon could be aimed in an oblique fashion. Nonetheless, the flight test and operational evaluation of the type proved troublesome and except for initial flight testing in 1937 where full armament was carried, the nacelle cannon armament and the accompanying gunner/loaders were eliminated in the final development aircraft.
World War II
Oberleutnant Rudolf Schoenert of 4./NJG 2 decided to experiment with upward firing guns in 1941 and began trying out upward-firing installations amidst scepticism from his superiors and fellow pilots. The first installation was made late in 1942, in a Dornier Do 17Z-10 that was also equipped with the early UHF-band version of the FuG 202 Lichtenstein B/C radar. In July 1942, Schoenert discussed the results of his experiment with General Kammhuber, who authorized the conversion of three Dornier Do 217J-1s to add a vertical armament of four or six MG 151s. Further experimentation was carried out by the Luftwaffe flight testing centre (Erprobungsstelle) at Tarnewitz on the Baltic Sea coast through 1942, and an angle of between 60° and 75° was found to give best results, allowing a target turning at 8°/sec to be kept in the gunsight.
Meanwhile, Schönert was made CO of II./NJG 5, and an armourer serving with the Gruppe, Oberfeldwebel Mahle developed a working arrangement with the unit's Messerschmitt Bf 110s mounting a pair of MG FF/M 20 mm (0.79 in) cannon in the rear compartment of the upper fuselage, firing through twin holes in the canopy's glazing. Schönert used such a modified Bf 110 to shoot down a bomber in May 1943. From June 1943 on, an official conversion kit was produced for the Junkers Ju 88 and Dornier Do 217N fighters. Between August 1943 and the end of the year, Schönert achieved 18 kills with the new gun installation.
Prior to the introduction of Schräge Musik in 1943, the Nachtjagdgeschwadern (NJG, night fighter wings) were simply equipped with heavy fighters fitted with radar in the nose and a combination of front-firing and defensive weapons. In the standard interception, the fighter approached the target from the rear to get into a firing position. This presented the night fighter's crew with a much smaller target area, and Royal Air Force bombers (such as the Whitley and Wellington medium bombers), in the years just before the war, had all been fitted with twin-gunned hydraulic tail turrets, and shortly thereafter with multi-gun tail turrets, to help fend off such attacks. The relatively small calibre .303 in (7.7 mm) machine guns used, however, did not provide adequate defensive firepower. The rear-gunners also maintained a watch for fighters and if warned the bomber pilots could pull evasive manouvres such as corkscrews. Night fighter pilots developed a new tactic to avoid the turret guns. Instead of approaching directly from the rear, they would approach about 1,500 ft (460 m) below the bomber. They would then pull up sharply and start firing when the nose of the bomber appeared in the gunsight. As the fighter slowed and the bomber passed over them, its wings were sprayed with cannon or machine gun rounds. This maneuver was effective, but difficult to perform. There was a significant risk of collision and if the bomb load exploded, it could take down the night fighter too.
Systems similar to the original Schräge Musik, such as the Sondergerät 500 or Jägerfaust, were tested on day fighters as well as a variety of other airframes, including the experimental Grosszerstörer (heavy destroyer). The Jägerfaust system, firing 50 mm (2 in) projectiles vertically into the lower sides of bombers, was triggered by an optical device. The pilot's only task was passing underneath the targeted bomber. The Jägerfaust was tested on the Fw 190, and was destined for installation in the Me 163B and the Me 262B. The definitive night fighter version of the Messerschmitt Me 262, the Me 262B-2, was also designed to carry such an installation, but the system did not work successfully, and it was not used operationally. Trials with the Komet, however, showed very promising results with six operational aircraft modified. On 10 April 1945, a Halifax bomber was shot down by Fritz Kelb flying a Jägerfaust-equipped Me 163B, most likely from I. Gruppe/JG 400 operating from Brandis, Germany.
As new experimental aircraft were developed for the night fighter role, such as the Horten Ho 229, the Schräge Musik system was incorporated from the outset. The experimental Horten Ho 229 flying wing series had an unusual upward-firing armament proposed for testing on the V4 night fighter prototype, photoelectric fired vertically mounted rockets or recoilless guns instead of cannon armament inspired by the Jagdfaust system's design.
- Dornier Do 217N: 4 × 20 mm MG 151/20
- Focke-Wulf Fw 189: 1 × 20 mm MG151/20 (used mainly on Eastern Front)
- Heinkel He 219: 2 × 30 mm MK 108
- Junkers Ju 88C/G: 2 × 20 mm MG 151/20
- Junkers Ju 388J: 2 × 30 mm MK 108
- Messerschmitt Bf 110G-4: 2 × 20 mm MG FF/M
- Messerschmitt Me 262B-2: 2 × 30 mm MK 108 (proposal only, B-2 version never produced)
- Focke-Wulf Ta 154: 2 × 30 mm MK 108
Method of sighting guns
In the Ju 88 G-6 night fighter, which was both fast and manouevrable, the Revi 16N gunsight was modified to allow the pilot to aim at the target by placing a reflecting mirror above the pilot’s head, parallel to a similar mirror placed behind the actual gunsight (where the eye would normally be), which itself was further to the rear, functioning together in the manner of a periscope. The Ju 88 G-6 was guided into position from sighting and final approach by commands from the radar operator, with the pilot only taking over when visual contact was made just prior to firing.
What a contrast with SCHRÄGE MUSIK! Again the technique was to approach deliberately at a lower level, but this time all the night fighter pilot had to do was slow up a little, rise up below the bomber and hold formation. An NJG experte could follow his observer's directions, acquire the bomber visually, close and destroy it within 60 seconds. The firing position, with the bomber 65° to 70° above the fighter, was an almost ideal one. The fighter could see the bomber clearly, as a darker silhouette either blotting out the stars or against paler sky or high cloud. It presented the biggest possible target and reflected any light from searchlights, ground fires or Tis [target indicators]. With the two aircraft in close formation, there was an ideal no-deflection shot. And the fighter was perfectly safe, because it was well below the Monica beam and could not be seen by any member of the bomber's crew. The only snag was that the Luftwaffe's guns were so effective that the night fighter usually had to get out of the way very fast. It was rather like 1916, except that a Lancaster with one wing blown off tumbled downwards and backwards faster than an ignited airship. [N 3]
Schräge Musik (or Schrägwaffen, as it was also called) was first used operationally during Operation Hydra (the first instance of the Allied bombing of Peenemünde) on 17/18 August 1943. [N 4] Three waves of aircraft bombed the area, and a successful diversionary raid on Berlin by RAF Mosquitoes attracted the main Luftwaffe fighter effort and meant that only the last of the three waves was met by any sizable group of night fighters. The two Groups of the third wave, 5 Group and the RCAF 6 Group, lost 29 of their 166 bombers, well over the 10% losses considered "unsustainable". In this raid, a total of 40 aircraft were lost: 23 Lancasters, 15 Halifaxes and two Short Stirlings.
Wide-scale adoption followed in late 1943, and by 1944, a third of all German night fighters carried upward-firing guns. Schräge Musik proved most successful in the Jumo 213 powered Ju 88 G-6. An increasing number of these installations used the more powerful 30 mm calibre, short-barreled MK 108 cannon, such as those retroactively fitted to the Heinkel He 219. By mid-1944, however, He 219 aircrew were criticizing the MK 108 installation because its low muzzle velocity and limited range meant that the night fighter had to be relatively close to the bomber to attack—with damage ensuing from debris. They demanded that either the MK 108s be removed and replaced by MG FF/Ms or the angle of the mounting be changed. Although He 219s continued to be delivered with the twin 30 mm mounted, these were removed by front line units. Using the Schräge Musik required precise timing and swift evasion; a fatally damaged bomber could fall directly upon the night fighter who had just shot it down if the fighter could not quickly turn away. The He 219 was particularly prone to this; its high wing loading at the edge of stalling speed, left it unmanouevrable, and the 61-victory night fighter ace Manfred Meurer lost his life 21/22 January 1944 when, after shooting down a Handley Page Halifax bomber, his He 219 was rammed by a Bf 110.
Schräge Musik allowed German night fighters to attack undetected, using special ammunition with a faint glowing trail replacing the standard tracers, combined with a "lethal mixture of armour-piercing, explosive and incendiary ammunition." Approaching from below provided the night fighter crew with the advantage that the bomber crew could not see the night fighter against the dark ground or sky, yet allowed the German crew to observe and identify the silhouette of the aircraft before they attacked. The optimum target for the night fighter was the wing fuel tanks, not the fuselage or bomb bay, because of the risk that exploding bombs would damage the attacker. “To overcome some of the problems, many NJG pilots closed the range at a lower level, below the Monica zone of coverage, until they could see the bomber above; then they pulled up into a climb with all front guns blazing. This demanded fine judgment, gave only a second or two of firing time and almost immediately brought the fighter up behind the bomber's tail turret.
Schräge Musik produced devastating results with its most successful deployment in the winter of 1943–1944. This was a time when losses became unacceptable: the RAF lost 78 of 823 bombers that attacked Leipzig on 19 February, and 96 of the 795 bombers that attacked Nuremberg on 30/31 March 1944. RAF Bomber Command was slow to react to the threat from Schräge Musik, with no reports from downed crews confirming the new menace in the skies. The sudden increase in bomber losses had often been attributed to flak. Initial reports from air gunners of German night fighters stalking their prey from below had appeared as early as 1943, but had been discounted. An urban myth developed around reports, made by RAF Bomber Command crews, who claimed "scarecrow shells" were encountered over Germany. The phenomenon was thought to be "AA shells simulating an exploding four-engined bomber and designed to damage morale. Sadly, in many cases these were actual 'kills' by Luftwaffe night fighters... It was not for many months that evidence of these deadly attacks was accepted." 
A detailed analysis of the damage done to returning bombers clearly indicated that the night fighters were firing from below. Defense against the attacks included mixing de Havilland Mosquito night fighters into the bomber stream, attempting to pick up radar emissions from the German night fighters. Wing Commander J.D. Pattinson of 429 "Bison" Squadron, recognized an unseen danger but to him, it "was all presumption, not fact." He ordered that the mid-upper turrets be removed and the "displaced gunner would lie on a mattress on the floor as an observer, looking through a perspex blister for night fighters coming up from below." While many Lancaster B. IIs had retained the FN64 ventral turret, a small number of Halifax and Lancaster bombers were unofficially fitted with a single machine gun[N 5] installation in either a ventral turret or a makeshift port directly under the mid-upper gunner station.
On this particular night the night fighters were to score heavily. The ground radar stations responsible for initial guidance to the vicinity of the bombers did their job well, as did the airborne radar operators to whom fell the task of final location of individual targets. The path of the returning bomber stream was clearly marked by the pyres of numerous downed victims. NJG-4 was operating from Gutersloh (later an RAF base) and in the space of 20 minutes, between 20.43 and 21.03, Schnaufer and his crew, using their upward firing cannons [from a Bf 110G night fighter], shot down seven Lancasters. As it was, on that black night, four night fighter crews accounted for 28 of the 62 bombers lost out of the 800 despatched.
In 1943, Commander Yasuna Kozono of the 251st Kōkūtai, Imperial Japanese Navy in Rabaul came up with the idea of converting the Nakajima J1N (J1N1-C) Irving into a night fighter. On 21 May 1943, at about the same time as the Luftwaffe's Oberleutnant Schoenert had his first victory with Schräge Musik in Europe, the field-modified J1N1-C KAI shot down two B-17s of 43rd Bomb Group attacking air bases around Rabaul. The Navy took immediate notice and placed orders with Nakajima for the newly designated J1N1-S night fighter design. This model was christened the Model 11 Gekko (月光, "Moonlight"). It required only two crew and like the KAI, had a twin 20 mm pair of Type 99 Model 1 cannon firing upward and a second pair firing downward at a forward 30° angle, placed in the fuselage behind the cabin, the model of 20mm calibre Japanese aircraft autocannon based on the Oerlikon FF, a close twin to the similarly-derived German MG FF weapon use to pioneer Schräge Musik for the Luftwaffe.
The Japanese Army Air Force's Mitsubishi Ki-46 "Dinah" twin engined fighter was used to test the Schräge Musik armament format in its Ki-46 III KAI version in June 1943, using a 37 mm Ho-203 cannon with 200 rounds of ammunition, the largest known calibre autocannon ordnance ever used for such an operational fitment. It was mounted in virtually the same position in the fuselage as in the Luftwaffe's own night fighters. Operational deployment began in October 1944.
One of the main Japanese fighters using this device was the Kawasaki Ki-45 "Nick". In addition to the aforementioned Schräge Musik installation on the IJNAF's Nakajima J1N1-S "Gekko" (two or three 20mm cannons firing upwards, some had two firing downwards), the Nakajima C6N1-S "Myrt" single-engined, high-speed reconnaissance aircraft was used with a pair of 20 mm Type 99 cannons.
One variant of the common A6M5 Zero single-seat fighter — the A6M5d-S variant — even had a single 20mm Type 99 cannon similarly mounted just behind the pilot, firing upwards for night fighter combat.
The Boulton Paul Defiant "turret fighter" was originally conceived under the F.9/35 specification for a "two-seat day and night fighter" to defend Great Britain against massed formations of unescorted enemy bombers. Regardless of the requirement, the use of its dorsal turret was predicated on the "broadside" fighter interception and combined fighter attack tactic in bomber interception. Attempts to take on single-seat fighters with Defiants led to catastrophic results in 1940 over France and during the Battle of Britain. With untenable losses in day operations, the Defiant was transferred to night fighting and there the type achieved some success. Defiant night fighters typically attacked enemy bombers from below in a similar manoeuvre to the later successful German Schräge Musik attacks, more often from slightly ahead or to one side, rather than from directly under the tail. During the winter Blitz on London of 1940–41, the Defiant equipped four squadrons, shooting down more enemy aircraft than any other type. The Defiant Mk II was fitted with AI.IV radar and a Merlin XX engine. A total of 207 Defiant Mk IIs were built, but the use of the turret fighter as a night fighter was short-lived as radar-equipped Beaufighter and Mosquito night fighters entered service in 1941 and 1942, respectively. Turret fighters with four 20mm cannon were specified under F.11/37, but got no further than a scaled prototype.
A Douglas Havoc, BD126, was fitted with six upward firing machine guns in the fuselage behind the cockpit. The guns could be controlled in elevation from 30 to 50 degrees and 15 degrees in the azimuth by the gunner in the nose. The aircraft was tested at the A&AEE in 1941 and thereafter, by the GRU and Fighter Interception Unit.
The American Northrop P-61 Black Widow night fighter could deliver a Schräge Musik–like surprise of its own, from below an enemy aircraft, because of the design of its remote dorsal turret carrying a quartet of .50 Caliber Browning M2 machine guns that could elevate to a full 90º position.
The Northrop F-89 Scorpion was originally designed to meet the 1945 United States Army Air Forces Army Air Technical Service Command specification ("Military Characteristics for All-Weather Fighting Aircraft") for a jet-powered night fighter to replace the P-61 Black Widow. The N-24 company proposal was armed with four 20 mm (.79 in) cannon in a unique trainable nose turret that could rotate 360˚ with the guns able to elevate to 105˚. Ultimately, the F-89 design abandoned the swiveling nose turret in favor of a more standard front-firing cannon arrangement.
In 1947, the United States Air Force tested a Schräge Musik gun installation on a Lockheed F-80A Shooting Star standard "day fighter" aircraft (s/n 44-85044) to study the ability to attack Soviet bombers from below. Twin 0.5 in (12.7 mm) machine guns were fixed in an oblique mount.
A final attempt to exploit a fully traversing turret was found in the original 1948 design of the Curtiss-Wright XF-87 Blackhawk all-weather jet fighter interceptor. Armament was to be a nose-mounted, powered turret containing four 20 mm (.79 in) cannon, but this installation was only fitted to the mock-up and never incorporated in the two prototypes.
Some Soviet jet fighter prototypes of the late-1940s/early-1950s era included cannon mounted in the nose that were capable of being trained in elevation, however none achieved production status.
The cause of losses... killed novice and expert crews impartially. This result contradicted the official dogma... I blame the ORS and I blame myself in particular, for not taking this result seriously enough... If we had taken the evidence more seriously, we might have discovered Schräge Musik in time to respond with effective countermeasures.—Freeman Dyson
- As a colloquialism, schräge can also translate as abnormal—as in the English queer.
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