two-seat heavy fighter, similar to ANT-401, but powered by two imported 597 kW (800 hp) Gnome-Rhône 14K engines and armed with two 100 mm recoilless rifles in outer wings, four fixed machine guns in the nose, and one flexibly mounted machine gun in the observers cockpit. One prototype, with Air Force designation DI-8 first flown in August 1935, but abandoned after abandonment of Leonid Kurchevsky's recoilless rifle projects and his subsequent arrest. ANT-48 – high-speed sport aircraft project. ANT-49 – proposed long-range reconnaissance variant with aerial cameras in the bomb bay and larger fuel tanks; project cancelled before a prototype was built. SB 2M-100 – first production model. Wing area increased to 56.7 m2 (610 ft2). Equipped with Klimov M-100 engines (the Hispano-Suiza 12Y built under licence) driving two-bladed propellers. SB 2M-100A – new M-100A engines of 642 kW (860 hp), driving three-bladed propellers. Produced from late 1936. Sometimes unofficially referred to as the SBbis. SB 2M-100A modernizirovannyi – new rear gun installation with MV-3 dorsal turret. Tested in May 1937. Accepted, but no production. SB-bis – prototype powered by 716 kW (960 hp) Klimov M-103 engines, dual controls and variable-pitch propellers. It flew in September 1937, but increased weight lead to reduced performance. SB-bis2 – M-103 powered prototype with polished wings. Little increase in performance. No production. SB-bis3 – third M-103 powered prototype, with new engine nacelles with radiators relocated under engines rather than the frontal radiators fitted in earlier aircraft. Tested from 1 November 1937 – 17 January 1938, with testing showing maximum speed increasing to 446 km/h (277 mph). Improvements later incorporated into production aircraft. SB 2M-103 — 10th series. 1938 production version with M-103 engines fitted with original frontal radiators and strengthened structure. Fitted with emergency flight controls for navigator, provision for retractable skis, and for two 368 litre external fuel tanks. SB 2M-103 – 14th series. Late 1939 production, with M-103 engine and revised nacelles and radiators as tested in SBbis3. SB 2M-103 – 18th series. Further improved production version, with fixed radiator intakes and partially polished wings. VISh-22 three-bladed variable-pitch propellers. Fitted with MV-3 dorsal turret. SB 2M-104 — Approximately 30–50 aircraft were completed with M-104 engines, but engine not in series production. SB 2M-106 — A few aircraft completed with M-106 engines, but engine not in production. USB – dual control trainer, with the instructor sitting in an open cockpit in the nose