Tupolev MTB-2

The Tupolev MTB-2 (Морской Тяжелый Бомбардировщик — Heavy Naval Bomber), also known as the ANT-44, was a four-engine prototype flying boat designed in the Soviet Union in 1935.

Design and development
The ANT-44 was designed as a long-range maritime reconnaissance/bomber flying boat. Construction of the first two prototype began in 1934. The initial design employed an all-metal construction with a shoulder-mounted semi-gull wing. The ANT-44 incorporated four 604 kW (810 hp) Gnome-Rhône Mistral Major 14Kdrs M-85 radial engines as well as under-slung stabilizing floats. After a month of factory trials, in December 1937 designers changed the Mistral Major radial engines for the higher rated and more powerful Tumansky M-87 627 kW (840 hp) engines. In 1938, they further modified the prototype to be amphibious, and the aircraft was refitted with updated 709 kW (950 hp) M-87A engines.

The second prototype, designated ANT-44bis or ANT-44D, was an amphibious aircraft powered by four M-87A engines. With I. M. Sukhomlin at the controls, the aircraft set several world records in its class:
 * 17 June 1940: altitude of 7,595 m (24,918 ft) without payload
 * 17 June 1940: altitude of 7,134 m (23,406 ft) with a 1,000 kg (2,205 lb) payload
 * 19 June 1940: altitude of 6,284 m (20,617 ft) with a 2,000 kg (4,409 lb) payload
 * 19 June 1940: altitude of 5,219 m (17,123 ft) with a 5,000 kg (11,023 lb) payload
 * 28 September 1940: maximum speed of 277.4 km/h (150 kn, 172 mph) over 1,000 km (540 nmi, 621 mi) with a 1,000 kg (2,205 lb) payload
 * 7 October 1940: maximum speed of 241.9 km/h (131 kn, 150 mph) over 1,000 km (540 nmi, 621 mi) with a 2,000 kg (4,409 lb) payload

Operational history
Only the two MTB-2 prototypes were built: the Soviet Union's entry into World War II interrupted any further development. Both aircraft were pressed into service in the Black Sea region. The ANT-44D piloted by I. M. Sukhomlin saw limited use in 1941–1943, both as a bomber and as a transport, and other special tasks, such as emergency supply flights.