Siemens-Halske O.H. was founded in 1847 to manufacture telegraphic equipment. It was not until 1873 that the more famous Siemens-Schuckert Werke title was adopted on the merging with the Schuckert works of Nurnberg to form the giant electrical combine.

The firm made a tentative excursion into the aircraft manufacturing field in 1907, when a non-rigid military airship was constructed at the request of the German General Staff. From 1909 to 1911 three original aircraft were built, the last bearing a close resemblance to the Bleriot monoplanes. Interest in aircraft manufacture then ceased until 1914, when, in response to urgent requests for aeroplanes from the German military forces, the aircraft department was reopened under the direction of Dr. Walter Reichel, assisted by Dr. Hugo Natalis, Wolff, the Steffen brothers (Franz and Bruno) and Forssman.

Initially "Giant" R (Riesenflugzeug) aircraft were designed and built, apart from the "Bulldog" monoplane, but towards the end of 1915 appeared the S.S.W. E 1, a neat shoulder-wing monoplane. It was accepted by Idflieg (Inspectorate of Flying Troops), and a small batch was built to bolster supplies of Fokker and Pfalz monoplanes. At this time the first French Nieuport scouts were enjoying a considerable success on the Western Front, and as there was no immediate prospect of Germany having a superior machine forthcoming, Idflieg requested the Albatros, Euler and S.S.W. firms to produce quickly an improved copy of the Nieuport as a means of obtaining parity with their opponents. Captured Nieuports were supplied to the firms as models, but Albatros did not make such a close copy of the French machine as did Siemens-Schuckert. Their machine closely resembled the Nieuports XI and XVII, differing noticeably only in the engine installation and, later, the tailskid arrangement. In October 1916 Bruno Steffen climbed to an altitude of 5,000 m. in 45 min. on the prototype Siemens-Schuckert D 1.

The D I was accepted for production, and on 25th November 1916 an initial order for 150 machines was placed. Production was somewhat tardy, airframes being held up for their engines-which were by way of being something new in geared rotaries-and a later order (21st March 1917) for 100 machines was cancelled, as it was found that by mid 1917 performance of the S.S.W. D I was no longer up to requirements. Eventually only 95 aircraft of the original order were completed; 22 by the Berlin factory and 73 at Nurnberg. A further 55 uncovered airframes were delivered to Adlershof.

Power unit of the D I was the Siemens-Halske Sh I geared rotary, which had been developed by yet another branch of the Siemens combine. This was an engine of considerable mechanical ingenuity, in which the crankcase rotated in one direction at about 900 r.p.m. and the crankshaft in the opposite direction at the same speed, thereby achieving a virtual engine speed of 1,800 r.p.m. for an airscrew speed of only 900 r.p.m. This resulted in greater propeller efficiency. Both 2 and 4 bladed propellers where used. The engine was mounted in an open-fronted horse-shoe-type cowling, which incorporated a front bearer spider and was cut away almost completely in the lower half to allow free escape of exhaust. The fuselage, based on four main longerons, was a slab-sided braced box-girder. The top decking was rounded both fore and aft of the cockpit, with light formers and stringers. With the lower longerons being set closer together than the upper pair, the sides tapered in, exactly as in the Nieuport model The foremost bay of the fuselage sides was covered with slightly bulged metal panels, which were embossed with large vertical ventilation louvres, the remainder was fabric covered.

Tail surfaces were all of steel-tube framing and fabric covered, the trapezoidal tailplane and unbalanced elevators being mounted directly on top of the top longerons. The balanced rudder was hinged to the sternpost and was of flattened comma profile. At a later date the underside of the tailplane was braced to the lower longerons with two steel-tube struts on either side.

The sesquiplane layout and swept-wing planform of the original French machine was retained, although the centre panel of the upper wing was simplified somewhat and the four centre-section struts were vertical in both side and front views. The wings were a normal braced structure based on two (upper) and one (lower) box spars; ribs in the upper wing panels being strengthened where necessary to act also as compression members. Ailerons were of light-gauge steel tube and of inverse taper; they were operated through a torque tube connected to bell cranks in the centre section. Both interplane and centre-section struts were of steel tube enclosed with wooden fairings.

A conventional vee-type undercarriage chassis was fitted, made up from streamlined steel tube and with the axle sprung with elastic shock cord. A hockey-stick type tailskid, pivoted about the lower longerons and internally sprung, was fitted to the first machines. Later the arrangement was modified and the tailskid attached to an inverted steel-tube pylon.

A further modification to the later production aircraft was the enclosing of the airscrew hub in a large pointed spinner, which considerably enhanced the lines of this already elegant aeroplane even though it did not materially improve its performance.

The only subsequent development of the S.S.W. D I was a single D ]a D3768/16, which had an increased wing area totalling 15-7 sq.m. Of the two D Ibs which had one-piece upper wings, D1230/17 had a further increase in total area to 16-2 sq.m., and D1231/17 was fitted with a highcompression Sh I engine, developing about 140 h.p. Area was again increased, to 19-2 sq.m., in an endeavour to achieve a good climb and altitude performance.

Many of the S.S.W. D Is were used by the flying schools, although small numbers appeared on the Western Front with Jastas 1-5 and 7, 9, 11 and 14. Two machines were delivered to the "Armee-Flugpark Sud".

TECHNICAL DATA

Description: Single-seat fighter.

Manufacturer: Siemens-Schuckert Werke G.m.b.H. Siemensstadt, Berlin und Nurnberg (Ssw.).

Power Plant: One 110 h.p. Siemens-Halske Sh I 9 cylinder geared rotary engine.

Dimensions: Span, 7-50 m. (24 ft. 71, in.). Length, 6-0 m. (19 ft. 81, in.). Area, 14-4 sq.m. (155-52 sq.ft.).

Weights: Empty, 430 kg. (946 lb). Loaded, 675 kg. (1,485 lb.).

Performance: Maximum speed, 155 km.hr. (96-875 m.p.h.). Climb, 1,000 m. (3,280 ft.) in 3-5 min., 2,000 m. (6,560 ft.) in 8-0 min., 3,000 m. (9,840 ft.) in 14-5 min., 4,000 m. (13,120 ft.) in 24-3 min. Duration, 231 hr.

Armament: One fixed Spandau machine-gun firing forward. Later twin machineguns were fitted.

Serials allocated for November 1916 order: D.3503 to D.3635/16 150.

D.3752 to D.3768/16

Serials allocated for March 1916 order: D.1230 to D.1329/17 100.