Design & Development

Throughout the 1930s, the air forces of the major military powers were engaged in a transition from biplane to monoplane designs. Most concentrated on the single-engine fighter aircraft, but the problem of range arose. The Ministry of Aviation (RLM, for Reichsluftfahrtministerium), pushed by Hermann Göring, issued a request for a new multipurpose fighter called the Kampfzerstörer (battle destroyer) with long range and an internal bomb bay. The request called for a twin-engine, three-seat, all-metal monoplane that was armed with cannon as well as a bomb bay. Of the original seven companies, only Bayerische Flugzeugwerke (Messerschmitt), Focke-Wulf and Henschel responded to the request.

Messerschmitt defeated Focke-Wulf, Henschel and Arado, and was given the funds to build several prototype aircraft. The Focke-Wulf design, the Focke-Wulf Fw 57, had a wing span of 25.6 m (84 ft) and was powered by two DB 600 engines. It was armed with two 20 mm MG FF cannons in the nose and a third was positioned in a dorsal turret. The Fw 57 V1 flew in 1936 but its performance was poor and the machine crashed. The Henschel Hs 124 was similar in construction layout to the Fw 57, equipped with two Jumo 210C for the V1. The V2 used the BMW 132Dc radial engines generating 870 PS compared with the 640 PS Jumo. The armament consisted of a single rearward-firing 7.92 mm MG 15 machine gun and a single forward-firing 20 mm MG FF cannon.

Messerschmitt omitted the internal bomb load requirement from the Ministry of Aviation directive to increase the armament element of the Ministry of Aviation's specification. The Bf 110 was far superior to its rivals in providing the speed, range and firepower to meet its role requirements. By the end of 1935, the Bf 110 had evolved into an all-metal, low-wing cantilever monoplane of semi-monocoque design featuring twin vertical stabilizers and powered by two DB 600A engines. The design was also fitted with Handley-Page wing slots(actually, leading-edge slats).

Early variants

By luck (and pressure by Ernst Udet), the Ministry of Aviation reconsidered the ideas of the Kampfzerstörer and began focusing on the Zerstörer. Due to these changes, the Bayerische Flugzeugwerke design better fitted the Ministry's requests. On 12 May 1936, Rudolf Opitz flew the first Bf 110 out of Augsburg. But, as many pre-war designs found, the engine technologies promised were not up to acceptable reliability standards. Even with the temperamental DB 600 engines, the Ministry of Aviation found that the Bf 110, while not as maneuverable as desired, was rather faster than its original request specified, as well as faster than the then-current front line fighter, the Bf 109 B-1. Thus the order for four pre-production A-0 units was placed. The first of these were delivered on January 1937. During this testing, both the Focke-Wulf Fw 187 and Henschel Hs 124 competitors were rejected and the Bf 110 was ordered into full production.

The initial deliveries of the Bf 110 encountered several delays with delivery of the DB 600 motors, which forced Bayerische Flugzeugwerke to install Junkers Jumo 210B engines, leaving the Bf 110 seriously underpowered and able to reach a top speed of only 431 km/h (268 mph). The armament of the A-0 units was also limited to four nose-mounted 7.92 mm MG 17 machine guns.

Even without delivery of the DB 600 engines, Bayerische Flugzeugwerke began assembly of the Bf 110 in mid-1937. As the DB 600 engines continued to have problems, Bayerische Flugzeugwerke was forced to keep on using Jumo motors, the 210G, which supplied 515 kW (700 PS) each (versus the 471 kW/640 PS supplied by the 210B). Three distinct versions of the Bf 110B were built, the B-1, which featured four 7.92 mm (.312 in) MG 17 machine guns and two 20 mm MG FF cannons. The B-2 reconnaissance version, which had a camera in place of the cannons, and the B-3 which was used as a trainer, with the cannons replaced by extra radio equipment. Only 45 Bf 110Bs were built before the Jumo 210G engine production line ended. The major identifier of the -A and -B-series Bf 110s was the very large "mouth" bath radiators located under each engine.

In late 1938, the DB 601 B-1 engines became available. With the new engine, the design teams removed the radiators under the engine nacelles and replaced them with water/glycol radiators for the C-series airframes onwards, placing them under the wing just outboard of each nacelle, otherwise similar in installation, appearance and function to those on the Bf 109E. With the DB 601 engine, the Bf 110's maximum speed increased to 541 km/h (336 mph) with a range of approximately 1,094 km (680 mi). A small oil cooler and air scoop remained under each engine nacelle for the remainder of the Bf 110's production run.

First conceived in the latter half of 1939, the D-series of Bf 110s was targeted to have improvements meant to increase its range. The initial D-series version, the Bf 110D-0 was designed to add a large, streamlined 1,050 litre (277 U.S. gallon) ventral fuel tank built under the fuselage, which required a substantially sized, conformal streamlined ventral fuselage fairing extending from halfway back under the nose to the rear of the cockpit glazing, inspiring the nickname Dackelbauch (dachshund's belly). The D-1 was also set up to accept a pair of fin-equipped 900 litre (238 U.S. gallon) drop tanks, one under each wing, increasing the total fuel capacity to 4,120 litres (1,088 U.S. gallons). The substantial added drag of the early "dachshund's belly" ventral fuselage tank in test flights mandated its omission from production D-1s although they were still prepared to mount an improved, better streamlined, version. D-1s so equipped were known as D-1/R1 whereas the D-1/R2 was equipped with two 900 l drop tanks and a droppable 85 liter oil tank. Later D-2 and D-3 versions retained the twin underwing 900 litre drop tank capability, using multipurpose ordnance racks capable of holding either drop tanks or carrying bombs.

Later production variants

FuG 220 and FuG 202 (centre) "Lichtenstein" SN-2 VHF band, and B/C UHF band night fighter radar antennas on the nose of a Bf 110 G-4 being serviced by Luftwaffe ground crew on Grove airfield, Denmark postwar in August 1945, before the aircraft was sent to the UK for research.

The production of the Bf 110 was put on a low priority in 1941 in expectation of its replacement by the Me 210. During this time, two versions of the Bf 110 were developed, the E and F models. The E was designed as a fighter bomber (Zerstörer Jabo), able to carry four 50 kg (110 lb) ETC 50 racks under the wing, along with the centreline ETC 500 bomb rack. The first E, the Bf 110 E-1 was originally powered by the DB 601B engine, but shifted to the DB 601P as they became available in quantity. A total of 856 Bf 110E models were built between August 1940 and January 1942. The E models also had upgraded armour and some fuselage upgrades to support the added weight. Most pilots of the Bf 110E considered the aircraft slow and unresponsive, one former Bf 110 pilot commenting the E was "rigged and a total dog."

The Bf 110F featured the new DB 601F engines which produced 993 kW/1,350 PS (almost double the power the original Jumo engines provided), which allowed for upgraded armour, strengthening, and increased weight with no loss in performance. Three common versions of the F model existed. Pilots typically felt the Bf 110F to be the best of the 110 line, being fully aerobatic and in some respects smoother to fly than the Bf 109, though not as fast. Eventually 512 Bf 110F models were completed between December 1941 and December 1942, when production gave way to the Bf 110G.

Bf 110G production details

Although the Me 210 entered service in mid-1941, it was plagued with problems and was withdrawn from service for further development. In the wake of the failure of the Me 210, the Bf 110G was designed. The G model was fitted with DB 605B engines, producing 1,085 kW (1,475 PS) at their Notleistung (war emergency) top-level setting, and 997 kW (1,355 PS) at 5.8 km (19,000 ft) altitude. The Bf 110G also had upgraded nose armament, and underwent some changes which improved the aerodynamics of the aircraft. The rear cockpit access was moved forward from the transversely-hinged, "tilt-open" rearmost canopy glazing to a side/top hinged opening section of the main canopy, opening to port, with a new rearmost framed glazing section fixed in place. No Bf 110 G-1 existed, so the Bf 110 G-2 became the baseline Bf 110G. A large number of Rüstsätze field conversion packs were available, making the G subtype the most versatile production version of the Bf 110.

The initial batch of six pre-series production G-0 aircraft built in June 1942 were followed by 797 G-2, 172 G-3 and 2,293 of the night fighter-dedicated, three-seater G-4 models; built between December 1942 and April 1945. Pilots reported the Bf 110G to be a "mixed bag" in the air, in part due to all changes between the G and F series. The Bf 110G was considered a superior gun platform with excellent all-around visibility, and considered, until the advent of the Heinkel He 219, to be one of the Luftwaffe's best night fighters.

Sources:
Gunston, Bill - The Encyclodepia of the Worlds Combat aircraft, 1976, Chartwell Books, Inc., New York
Brown, Eric, Captain - Wings of the Luftwaffe, 1979, Airlife Publishing Ltd., Shrewsbury
Gunston, Bill & Wood, Tony - Hitler's Luftwaffe, 1977, Salamander Books Ltd., London
Donald, David - The Complete Encyclopedia Of World Aircraft, 1997, Brown Packaging Books Ltd., London
Wikipedia - BF 110