The design originated in 1936 with the MB-170.01 two-seat fighter, which flew for the first time on 15 February 1938 with two 708-kW (950-hp) Gnome-Rhone 14N-6/7 radials and an underfuselage cupola intended for defensive armament or reconnaissance equipment, but the undercarriage collapsed on landing a month later. On 30 July the three-seat MB-170-02 was air-tested. The M.B.170.02 second prototype was configured as a pure bomber without the cupola but with an extensively glazed nose and larger vertical surfaces for improved directional stability.
Several operational variants were proposed, but the only types to enter service in World War II were the M.B.174 reconnaissance and attack bomber, and the M.B.175 light bomber.
Further development led to the Bloch 174.01, which flew on 5 January 1939 and series production at three SNCASO factories was ordered the following month. The M.B.174 prototype had 768-kW (1,030-hp) 14N-20/21 engines and revised accommodation, leading to the definitive model with more power and a number of refinements.
The MB-174 was a low-wing monoplane with two 850kW Gnome-Rhone 14N-48/49 radial engines in close-fitting cowlings. It had twin fins and rudders of oval form. The nose was extensively glazed, and pilot and dorsal gunner were accommodated under a raised glazed canopy. Defensive armament comprised two fixed forward-firing wing machine-guns, twin guns on a flexible mounting at the rear of the crew canopy and three further guns ventrally mounted to fire to the rear. All machine-guns were of the 7.5mm MAC 1934 type.
56 Bloch 174 A3 reconnaissance aircraft had been completed by the time of the June 1940 capitulation.
The MB-174 was developed into the MB-175 B3 bomber, with an enlarged bomb bay capable of carrying a maximum of 600kg of bombs, requiring a new centre section.
Only 20 had been accepted when the Germans took over deliveries, using 56 MB-175s as trainers. The French Navy took delivery of a post-war MB-175T torpedo-bomber version, 79 being built.
Engines: 2 x Gnome-Rhone 14N-6/7 radial, 708-kW (950-hp).
Reconnaissance and attack bomber.
Span: 17.9m (58ft 8.75 in)
Length: 12.25m (40ft 2.25in).
Engines: 2xGnome-Rhone 14N-48/49, 820kW (1,100 hp).
Armament: 7x7.5-mm (0.295-in) MAC machine-guns plus provision for up to 400kg (8812 lb) bombs internal
MTOW: 7160 kg (15,784 lb).
Max speed: 329 mph at 17,060 ft.
Operational range: 802 miles with max bombload.
Take-off weight: 7160 kg / 15785 lb
Wingspan: 17.92 m / 58 ft 10 in
Length: 12.23 m / 40 ft 1 in
Max. speed: 530 km/h / 329 mph
Range: 2000 km / 1243 miles