The Siebel Si 204 is a German, twin-engine, multi-role, semi-shell aircraft, all-metal, low-wing design. The drive was made of two Argus As 410 engines with a maximum power of 360 HP. The single-spar wing was equipped with crocodile flaps powered by an electro-hydraulic mechanism. The shuttlecocks were covered with linen. The hull had a cross-section similar to a rectangle rounded at the top. The crew cabin with two seats was located at the front of the fuselage. A passenger cabin with eight seats was placed in the fuselage. The cabin entrance door was on the left side of the fuselage. The vertical tail was doubled, the rudder had horn compensation. The ballasts were covered with sheet metal, while the moving parts were covered with linen. The electro-hydraulic retractable landing gear was retracted to the rear in the engine nacelles. Siebel Si-204V1 was flown on May 23, 1941. The aircraft entered serial production with the designation Si-204A-1. A year later, the Si-204D version was tested, which received a new, fully glazed front with the crew cabin inscribed in the longitudinal contour of the fuselage. The aircraft was powered by two Argus As 411 engines with a take-off power of 580 KM, equipped with biplane propellers. These planes were used extensively in aviation schools. The machine took two members, five apprentices as well as special navigational or radar equipment and, if necessary, a small bomb load. These airplanes were mainly used for groundless pilot training, navigation, and also as a flying lecture hall for candidates for radio operators. The Si-204 V22, V23 prototypes and the Si-204E-O aircraft were equipped with a 01 131 dorsal shooting turret with a single 13mm MG 131 machine gun. These planes could carry a bomb load of up to 1000 kg on external hooks. It was also planned to start production of the Si-204D-3 variant with wings, vertical and horizontal tail of an all-wooden structure. The production of Si-204 aircraft was carried out by the SNCAC factory in France (168 in total, of which the Luftwaffe took over 147) and the Aero (515) and MBB (491) plants in the Protectorate of Bohemia and Moravia. Numerous Si-204 planes fell into the hands of the victorious Allies. Apart from the Soviet Union, Great Britain has acquired the greatest number of aircraft of this type. About twenty Si-204 aircraft were on the territory of Switzerland. In the Netherlands, the Si-204D aircraft served as a flying laboratory after the war. After the war, the production of Si-204D was continued by the Aero plant in Prague, which produced a total of 172 copies of these machines under the designation C-3 and C-103. SNCAC plants in France also continued production of the Si-204, the Si-204 aircraft were designated Nord NC-701, and the Si-2O4A Nord NC-702. Both types were called Martinet. French aircraft were equipped with Renault12S engines, which are the equivalent of Argus As 411 A1 engines with a three-blade, metal, self-adjusting Ratier propeller with a diameter of 2.65 m. In total, 350 copies of these aircraft were produced in France after the war. Air France used 31 Martinets, six NC702s were used to transport mail from late 1946, and six more machines in the air-photogrammetric version were used by the National Geographic Institute. Most of the Martinets, however, were taken over by the French military aviation, which used them as transport aircraft, among others in the fighting in Vietnam. Specifications: length: 13m, wingspan: 21.33m, height: 4.25m, maximum speed: 364km / h, climb speed: 6m / s, practical ceiling: 6400m, maximum range: 1400km.