In World War II, Schräge Musik was the name Germans gave to upward-firing autocannon that the Luftwaffe mounted in night fighter aircraft. A similar fitment was used by 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 air arm had their first victories with fighter-mounted upward-firing autocannons in May 1943.
Schräge Musik derives from the contemporary German colloquialism for shaky, off-tune music; literally, it translates to slanted or oblique music.
Night fighters used this device to approach and attack Allied bombers from below, outside the bomber crew's usual field of view or fire. Most of the Allied bomber types of that era which were used for nocturnal bombing missions (primarily the Avro Lancaster) lacked effective ventral armament, leaving them easy prey to attacks from below, an advantage the Luftwaffe capitalized on.
An attack by a Schräge Musik-equipped fighter was typically a 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, pusher configured fighter aircraft with flexibly mounted forward-firing machine guns enabled gunners to discover the principle of zero deflection shooting in which the fall of fire appears to follow a straight rather than curved path, greatly simplifying the business of hitting a moving target from a moving weapon platform.
When later, conventionally arranged, single-seat biplanes featured machine guns mounted on the top wing to fire over the disk of the propeller (in the absence of deflector plates or synchronization gear), arrangements had to be made to reload a weapon otherwise limited in flight to a single magazine. The Foster mounting used with air-cooled Lewis guns not only allowed the guns to be drawn and tipped back to reload but also be "locked at any angle within a 90° arc from horizontal to vertical". Whether by accident or design, this feature allowed the guns to be locked at 45° elevation, an 'ideal' angle at which the ballistic properties of World War I rifle-calibre guns and typical biplane aircraft speeds combined to give the appearance of shooting straight and true. This is illusory since, seen by an objective observer, the bullet's true path is a parabola (but so modified by the relative movement of the aircraft that shots appear to follow a straight line). Since shots taken at that angle generally hit their mark, requiring no calculation, compensation, deflection or 'aiming off', it was common for the guns of the Nieuport 11 and Nieuport 17 fighters, especially in British service, and Royal Aircraft Factory S.E.5 to be so arranged, allowing attacks to be made on enemy bombers or reconnaissance aircraft from the "blind spot" below the tail.
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: with his upper-wing-mounted machine gun in his SE.5, pulled down on its ratchet tracks at an angle of 45°, Ball was able to shoot down the enemy from below. (Ball also mounted another machine gun in the bottom of the cockpit to fire downward) Among many other RFC and French combat aircraft, the Nieuport 17 used an arrangement of Le Prieur rockets mounted obliquely to the interplane struts, 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 German bomber and airship raids over Great Britain. The armament of two Lewis guns was mounted on twin Foster mountings, in preference to the synchronized Vickers preferred for day fighting. These were located at the upper center-section or fixed to fire upwards in a position that both eliminated the need for 'deflection' shooting and prevented the pilot from losing night vision from the flash of the firing guns.
The Sopwith Dolphin, a "multi-gun" fighter design which entered service near the end of World War I, was armed with two forward-firing Vickers machine guns in the usual location, just forward of the cockpit, but could also carry a pair of Lewis machine guns on the forward cross-tube of the cabane strut structure, aimed forwards and upwards, as an anti-Zeppelin armament scheme, and were so equipped on delivery from the makers. 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 altitude was the abortive Supermarine/Pemberton-Billing P.B.31E Nighthawk, the first project of the Supermarine Aviation Works Ltd. This 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 1 1⁄2-pounder (37 mm) recoilless Davis gun mounted above the top wing, 20 shells that had a wide arc of fire and upward elevation, two .303 in (7.7 mm) Lewis guns and a trainable nose-mounted searchlight.
First flown in February 1917, the lumbering fighter could only manage 60 miles per hour (97 km/h) at 6,500 feet (2,000 m) and took an hour to climb to 10,000 feet (3,000 m), which was inadequate for intercepting Zeppelins. Unsurprisingly, the project was summarily dropped.
The Boulton Paul Bittern was a twin-engined night fighter (designed to Specification 27/24) with an armament 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 tested on the Airco DH.4. The cannon fired 23-ounce (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 and fire 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 1]
Similar logic lay behind the later Vickers Type 414 twin-engined fighter. This aircraft, which can be seen a natural successor to the Vickers COW gun fighter, combined a streamlined monoplane two-seater fighter airframe with a remotely controlled nose-mounted 40mm cannon that could be elevated for no-allowance shooting.
While turret fighters like the Boulton Paul Defiant and the naval Blackburn Roc addressed the same threat - enemy bombers attacking the UK - the approach was very different: upward-firing guns and no-allowance shooting are separate and distinct, the equipment that can do the one can, generally speaking, be arranged so as to do the other (unless the fixed armament is automatically triggered, as in the photo-cell firing arrangements detailed below). On paper at least, the advantages of flexible aim and weight of fire from a two-seater were clear: the pilot is not overburdened, several fighters could be brought to bear on a target together and there are two pairs of eyes per aircraft. However, the weight of a powered turret and air gunner imposed their own severe and often fatal penalties.
The RAF put the Defiant into service in 1939, intending to use it against bombers, despite the bombers' numerous gun positions; however, it quickly became apparent that bombers escorted by nimble single-engined fighters bought within range by the speed and unprecedented territorial gains of blitzkrieg could not be engaged effectively. Despite being utterly outclassed as a day fighter, when moved to the night-fighter role it had some success, typically attacking from below and slightly ahead of the bomber, well outside its field of defensive fire.
Meanwhile, 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 slewed, aimed and fired at an oblique angle but flight tests and operational evaluation, disproved the theory: 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
Air Ministry Specification F.9/37 led to the second, Rolls Royce Peregrine powered, prototype of the Gloster G39 having a +12°, no-allowance armament of three upward-firing dorsal 20mm cannon in the fuselage and two in the nose. While it was a promising aircraft in its own right, by the time that the second prototype was completed the conventionally-armed Bristol Beaufighter was already in production, so neither the G39 nor the subsequent Gloster Reaper were pursued.
Similar logic lay behind Air Ministry specification F11/37, which specified a turret-mounted cannon armament: of three companies who tendered (Armstrong Whitworth and Bristol) had turrets that could only traverse through the forward hemisphere, as did Air Ministry specification F22/39, written around the Vickers Type 414 twin-engined fighter, which combined a streamlined monoplane two-seater fighter airframe with a remotely controlled 40mm cannon in the nose that could be elevated for no-allowance shooting.
Oberleutnant Rudolf Schoenert of 4./NJG 2 decided to experiment with upward-firing guns in 1941 and began trying out upward-firing installations, amid 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 experiments were carried out by the Luftwaffe flight testing centre Erprobungsstelle) at Tarnewitz on the Baltic Sea coast through 1942. An angle between 60° and 75° was found to give best results, allowing a target turning at 8°/sec to be kept in the gunsight.
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, 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.
Before 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, presenting the night fighter crew with a much smaller target, a problem compounded by the Royal Air Force bombers (such as the Whitley and Wellington medium bombers) first being fitted with twin-gun hydraulic tail turrets, later uprated to four guns to fend off just such attacks.
While the small .303 in (7.7 mm) calibre made these guns less effective than hoped, rear-gunners also maintained a watch for fighters and, if warned, the pilot would make evasive manoeuvres such as corkscrews. Night-fighter pilots therefore 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, 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. While effective, this manoeuvre was difficult to perform, there was a risk of collision and, if the bomb load exploded, it could also destroy the attack aircraft.
Systems similar to the original Schräge Musik, such as the Sondergerät 500 or Jägerfaust, were tested on day fighters and other airframes, with the largest-calibre upward-firing aerial ordnance in German service, based on the quintuple-launcher of the 21 cm Nebelwerfer infantry barrage rocket, the experimental heavy-bomber based Grosszerstörer (heavy destroyer) also under test.
The Jägerfaust system, firing 50 mm (2 in) projectiles vertically into the lower sides of bombers, was triggered by an optical device, so the pilot's only task was to pass beneath the target. This 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 was a failure and it was not used operationally. Trials with the Komet were promising, 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 probably from I. Gruppe/JG 400 operating from Brandis, Germany.
As experimental aircraft were developed as night fighters, such as the Horten Ho 229, a Schräge Musik system was incorporated from the outset. The experimental Horten Ho 229 flying wing series was proposed for consideration, with a form of unusual upward-firing armament for testing on the V4 night fighter prototype, photoelectric fired vertically mounted rockets or recoilless guns, instead of cannon armament inspired by the Jagdfaust.
- 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 manoeuvrable, the Revi 16N gunsight was modified to allow the pilot to aim at the target, by placing a reflecting mirror above the his head, parallel to a similar mirror placed behind the gunsight (where the eye would normally be), which 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 2]
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 the night of 17/18 August 1943. [N 3] Three waves of aircraft bombed the area and a diversion on Berlin by RAF Mosquitoes, attracted the main Luftwaffe fighter effort and meant that only the last of the three waves was met by many night fighters. Number 5 Group and RCAF 6 Group in the third wave, lost 29 of their 166 bombers, well over the 10 percent losses considered "unsustainable". In this raid 40 aircraft were lost: 23 Lancasters, 15 Halifaxes and two Short Stirlings.
Adoption of Schräge Musik began 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-millimetre (1.2 in) calibre, short-barrelled MK 108 cannon, such as those fitted to the Heinkel He 219, fully contained within the fuselage. By mid-1944, He 219 aircrew were critical of the MK 108 installation, because its low muzzle velocity and limited range, meant that the night fighter had to be close to the bomber to attack and be vulnerable to damage 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 on the night fighter, 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 unmanoeuvrable.
Schräge Musik allowed German night fighters to attack undetected, using special ammunition with a faint glowing trail replacing the standard tracer, 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 them against the dark ground or sky, yet allowed the German crew to see 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 judgement, 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 Bomber Command losses became unsupportable: 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 shot-down crews reporting the new tactic; the sudden increase in bomber losses had often been attributed to flak. Reports from air gunners, of German night fighters stalking their prey from below had appeared as early as 1943 but had been discounted. A myth developed among RAF Bomber Command crews that "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. 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 showed that the night fighters were firing from below. Defence against the attacks included mixing de Havilland Mosquito night fighters into the bomber stream, 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 machine-gun, normally of .303 calibre but Canadian units tended to use the 0.50-inch (12.7mm) heavy machine gun. (If not installed in a ventral turret these weapons were mounted in 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 the 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 20-millimetre (0.79 in)-calibre twinned pair of Type 99 Model 1 cannon firing upward and a second pair firing downward at a forward 30° angle, also placed in the fuselage behind the cabin. The Type 99 20mm calibre autocannon ordnance used by Japanese aircraft was based on the drum-magazine fed Swiss Oerlikon FF ordnance, a close twin to the German MG FF weapon, used to pioneer Schräge Musik for the Luftwaffe.
The Japanese Army Air Force 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 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". With the 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—had a 20mm Type 99 cannon 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 based on the "broadside" fighter interception and combined fighter attack tactic of 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 such high 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 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 1940–1941, 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 Defiant was retired as radar-equipped Beaufighter and Mosquito night fighters entered service in 1941 and 1942. 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 30–50 degrees and 15 degrees in the azimuth by the gunner in the nose. The aircraft was tested at the A&AEE in 1941 and then 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, 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 90° 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
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