In the early 1930s the Germans resorted to clandestine measures to obtain modern military aircraft. Accordingly, the Heinkel He 111 had been ostensibly designed by Walter and Siegfried Gunter as a fast commercial transport for the German airline Lufthansa. Like the famous He 70, it was a radically streamlined, all-metal aircraft with smooth skin and elliptical wings. Early models, both civil and military, also featured a stepped cabin with a separate cockpit enclosure. The new bomber proved fast and maneuverable, so in 1937 several were shipped off to the Spanish Civil War for evaluation. Not surprisingly, the He 111s outclassed weak fighter opposition and flew many successful missions unescorted. Thereafter, German bomber doctrine called for fast, lightly armed aircraft that could survive on speed alone. That decision proved a costly mistake in World War II. In 1939 the Model P arrived, introducing the trademark glazed cockpit canopy that appeared on all subsequent versions. When war finally erupted that fall, the fast, graceful Heinkels constituted the bulk of Germany’s bomber forces.
Although the Heinkel He 111 was designed ostensibly as a civil airliner for Lufthansa, its military potential was of a far greater importance. The first prototype of Siegfried and Walter Gunter’s enlarged, twin-engine development of the remarkable He 70 was fitted with a glazed nose when flown at Rostock-Marienehe on 24 February 1935, in the hands of Flugkapitan Gerhard Nitschke. An all-metal cantilever low-wing monoplane, it was powered by two 660 hp (492 kW) BMW VI 6,OZ engines and was followed by two further prototypes, each with shorter-span wings than those fitted on the first prototype. The third aircraft became the true bomber prototype and the second, which flew on 12 March 1935, was a civil version with a mail compartment in the nose and two passenger cabins, with seats for four and six passengers. After tests at Staaken this prototype eventually joined the Lufthansa fleet, although much of the development work on the civil version was carried out by the fourth prototype, the first to be revealed to the public and demonstrated at Berlin’s Tempelhof Airport on 10 January 1936. Lufthansa received six He 111C 10 seat airliners during 1936, and these first entered service on the Berlin-Hannover-Amsterdam, Berlin-Nuremberg-Munich and Berlin-Dortmund-Cologne routes. Lufthansa received later a number of He llIG-3 transports with 880 hp (656kW) BMW 132Dc engines and, later, a further generally similar hatch under the alternative designation He 111L.
Development of the military counterpart continued with the manufacture of 10 He 111A-0 pre-production aircraft, based on the third prototype, but with a longer nose and armed by three MG 15 machine-guns in nose, dorsal and ventral positions. Two were used for operational trials at Rechlin but poor handling, power deficiencies and inadequate performance resulted in rejection, and all 10 were later sold to China. The solution was the installation of two 1,000-hp (746-kW) Daimler-Benz DB 600A engines, first fitted to the fifth (B-series) prototype which flew in early 1936 as the forerunner of the first production versions built at Marienehe from the autumn of 1936. These comprised the He 111B-1 powered by the 880-hp (656-kW) DB600, followed by the He 11IB-2 with 950-hp (708-kW) DB 600CG engines. The improvement in the performance of these aircraft resulted in the Reichsluftfahrtministerium placing such large orders that it was necessary to build a new He 111 construction facility at Oranienburg, near Berlin, this being completed in 1937.
The B-series was followed by the He 111D-1 with improved DB 600Ga engines, but the urgent need to divert DB 600 powerplant for fighter production meant that this version was built in only small numbers. This brought introduction of the 1,000 hp (746 kW) Junkers Jumo 211A-1, installed initially in a He 111D-O airframe to serve as the prototype of the He 11IE-0 pre-production series. In the initial production He 11IE-1 bomber of February 1938 the bombload was increased to 3,748 lbs (1700 kg), but the He 11IE-3 had another increase to 4,409 lbs (2000 kg), and the ensuing He 11IE-4 could carry 2,205 lbs (1000 kg) of this total on underfuselage racks; final sub-variant of the E-series, the He 111E-5 introduced an additional 183.7 Imp gal (835 litres) of auxiliary fuel carried within the fuselage. The next version into production was the He 111G which first introduced a new wing of simplified construction with straight, instead of curved taper. This was used first in the He 111G-3 civil transport built for Lufthansa, and there was some delay before it was approved by the RLM. Then followed the He 111G-1, basically similar to C-series aircraft but for the addition of the new wing, and the He 111G-4 which was powered by the 900 hp (671 kW) DB 60OG engine; four He IIIG-5 aircraft supplied to Turkey had Daimler-Benz 600Ga engines. Next came, unsequentially, the similar He 111F-1 powered by Jumo 211A-3 engines of which 24 were supplied to Turkey, and 40 virtually identical aircraft were built for the Luftwaffe in 1938 under the designation He IIIF-4.
First deliveries to an operational squadron were made late in 1936, to 1./KG 154 at Fassberg, and in February 1937 30 He 111B-ls were sent to the Legion Condor bomber unit K/88 in Spain, following operational trials in which four of the pre-production He 11IB-Os were flown by a flight of VB 88. The He 111 bore the brunt of the Luftwaffe’s bombing effort in early World War 11. Poland in the autumn of 1939, Norway and Denmark in April 1940, France and the Low Countries in May and against British targets during the Battle of Britain. Large-scale introduction of the Junkers Ju 88, and the He 111’s vulnerability to British fighters, resulted in the Heinkel bomber being transferred to night operations and to a variety of specialised roles, as a missile-carrier, torpedo-bomber, pathfinder and glider- tug. Transport duties were also undertaken, including operations to supply the beleaguered German army at Stalingrad between November 1942 and February 1943, and by the end of the war He Ills were virtually flown only in the transport role. Production of more than 7,000 German-built aircraft for the Luftwaffe was completed in the autumn of 1944. In addition to those manufactured in Heinkel factories at Marienehe and Oranienburg, He Ills were built by Norddeutsche Dornierwerke in Wismar, by Allgemeine Transport-gesellschaft in Leipzig, Arado in Babelsberg and Brandenburg/Havel and at other centres. Some 236 He 111Hs were built by CASA in Spain during and after the war as the CASA 2.111, approximately 130 with Jumo 21IF-2 engines and the rest with Rolls-Royce Merlin 500-29s. Some were converted later for transport and training duties.
Following unsatisfactory tests of 10 pre-production He 111A-0 bombers, all were sold to China.
Testing of the fifth prototype with 746 kW (1,000 hp) DB 600A engines led in 1936 to the production He 111B-1 with 656 kW (880 hp) DB 600C engines, followed by the He 111B-2 with the 708 kW (950 hp) DB 600CG.
Six 10-passenger airliners for Lufthansa.
An improved version with DB 600Ga engines and auxiliary wing radiators deleted; production was discontinued in favour of the He 111E.
The shortage of DB 600 engines brought installation of 746 kW (1,000 hp) Junkers Jumo 211A-1 engines in an He 111D-0 airframe; the resulting He 111E-0 pre-production prototype had increased bombload; production He 111E-1 bombers were delivered in 1938, followed by the He 111E-3 and He 111E-4 with further increase in bombload and He 111E-5 with fuselage auxiliary fuel tank.
The new wing of the He 111G and Jumo 211A-3 engines characterised the 24 He 111F-1 bombers supplied to Turkey; the Luftwaffe received 40 similar He 111F-4 aircraft in 1938.