In late 1936 SNCASO initiated the contract of a two/three-seat multi-role bomber which it identified as the Bloch M.B.170. Under the direction of Bloch's Chief Designer Henri Deplante, the design and building of the prototype progressed but as a result of indecision by the Armée de I'Air this took three years to evolve into the Bloch 174 A.3 reconnaissance and target-marking aircraft, with secondary capabilities as a bomber.

The M.B.170.01 prototype flew for the first time on 15 February 1938. It was of cantilever low-wing monoplane configuration, and the wing and tail-plane both had marked dihedral, the latter carrying twin end plate fins and rudders. Landing gear was of the retractable tailwheel type, and the powerplant comprised two 950 hp (708 kW) Gnome-Rhône 14N-6/7 radial engines. The prototype featured an unusual cupola mounted beneath the fuselage, and intended to house a camera for use in the reconnaissance role, or alternatively to provide an additional position for a defensive gun. When the M.B.170.01 prototype was damaged as the result of a crash-landing, a second rather different M.B.170.02 prototype continued the flight test programme. This was configured to serve essentially as a high-speed bomber. The under-fuselage cupola was deleted, the undersurface of the forward fuselage was extensively glazed, and the tail unit was provided with fins and rudders of increased area.

A Three-sided view of the Bloch M.B.174 A.3 Reconnaissance Bomber
 

While this programme had been in progress, the design team had evolved a series of variants for differing roles, and allocated the identifications M.B.171, M.B.172, M.B.173 and M.B.174. It was this last proposal which aroused the interests of the French air ministry, leading To construction of the MB.174.01 prototype, which flew for the first time on 5 January 1939. This differed yet again, with the crew accommodation and glazed canopy moved further aft, the fuselage nose extensively glazed, and powerplant comprising two 1,030 hp (768 kW) Gnome-Rhône 14N-20/21 engines. Six pre-production examples of this version were ordered before flight testing began, but there was no need for recriminations from the French Air Ministry, as the test programme proceeded smoothly, without any major problems. In consequence an order for an additional 50 production aircraft was placed.

The pre-production and production aircraft all had more powerful Gnome-Rhône 1,100 hp (820 kW) 14N-48/49 engines, but early testing of the first pre-production aircraft showed that the cooling of these engines was only marginal, leading to a reduction in the diameter of the propeller spinners to allow an increased air-flow to the engine cylinders. Just before the first examples were delivered to units, it was decided to modify the defensive armament as a result of early combat experience with other types, and it was not until mid-March 1940 that the first M.B.174 A.3 production aircraft were delivered to Groupe de Reconnaissance II/33. By the time production of the M.B.174 A.3 stopped in May 1940 a total of 50 had been delivered to operational units.

The first operational sortie was flown on 29 March 1940 by the famed Capitaine Antoine de Saint-Exupery. As it had an insignificant bombload the M.B.174 A.3 made little impact on the Blitzkrieg, but performance and handling were so outstanding and made such a difference to the casualty-rate among squadrons equipped with the type, that the Bloch M.B.175 B.3 was hurriedly planned as a purpose-designed bomber capable of carrying 1,323 lbs (600kg) of bombs. Altogether 25 Bloch M.B.175 B.3s were completed before France collapsed. with more than 200 on the production line. Had France been able to resist longer the 175 would have been a potent weapon. It was only in 1942 in Tunisia, North Africa that the survivors (M.B.174s) were fitted to conduct shallow dive-bombing with bombs of up to 1,102 lbs (500 kg).

Groupes I/33, I/52, and II/36 each received examples during the following month, and early operational experience with these aircraft proved them to be an excellent type for deployment in a reconnaissance role, sufficiently fast and manoeuvrable at altitude to be able to elude Luftwaffe interceptors. When the collapse of France was imminent, many of the M.B.174s in use with squadrons were destroyed to prevent their capture, but despite this a number remained in service with the Vichy French air force in Tunisia until after VE-Day. Additionally, isolated examples were used for development projects for two or three years after the war's end.

A few M.B.174 A.3 and M.B.175 B.3 aircraft saw service with the Luftwaffe, but most served with Vichy France in North Africa and many survived the war. Indeed the torpedo-carrying M.B.175 T remained in production for the Aéronavale until 1950. Ironically, in March 1941, the Germans used the same engines of the Bloch M.B.175 to power the Messerschmitt Me 323 Gigant cargo transport, some of which actually flew with engines, cowlings and propellers taken from Bloch M.B.175s already completed.

Variants

Bloch M.B.170.01 - The M.B.170.01 prototype flew for the first time on 15 February 1938. The prototype featured an unusual cupola mounted beneath the fuselage, and intended to house a camera for use in the reconnaissance role, or alternatively to provide an additional position for a defensive gun. the powerplant comprised two 950 hp (708 kW) Gnome-Rhône 14N-6/7 radial engines.

Bloch M.B.170.02 - When the M.B.170.01 prototype was damaged as the result of a crash-landing, a second rather different M.B.170.02 prototype continued the flight test programme. Configured to serve essentially as a high-speed bomber, the under-fuselage cupola was deleted, the under surface of the forward fuselage was extensively glazed, and the tail unit was provided with fins and rudders of increased area.

Bloch M.B.174.01 - The MB.174.01 prototype, which flew for the first time on 5 January 1939, differed yet again, with the crew accommodation and glazed canopy moved further aft, the fuselage nose extensively glazed, and powerplant comprising two 1,030 hp (768 kW) Gnome-Rhône 14N-20/21 engines. Six pre-production examples of this version were ordered before flight testing began, but with Gnome-Rhône 1,100 hp (820 kW) 14N-48/49 radial engines.

Bloch M.B.174.01 A.3 - With successful testing of the pre-production aircraft, an order for 50 production aircraft was placed. They used the same Gnome-Rhône 1,100 hp (820 kW) 14N-48/49 engines of the pre-production aircraft, but incorporated a smaller propeller spinner after cooling problems with the pre-production models. Just before delivery to operational units, the defensive armament was modified. Capable of carrying 882 lbs (400 kg) of light bombs, it was later modified to carry a single 1,102 lbs (500 kg) centreline bomb.

Bloch M.B.175 B.3 - The M.B.174.01 A.3 proved itself a very outstanding aircraft in performance during the initial stages of the Blitzkrieg, but its 882 lbs (400 kg) bomb load was found lacking. A hurried redesign to incorporate a bomb load of 1,323 lbs (600 kg) led to the development of the M.B.175 B.3 which was to be built as a dedicated bomber. 25 aircraft had been completed when France fell, with another 200 aircraft still on the production line. Bomb load usually consisting of three 441 lbs (200 kg) or a single 1,102 lbs (500 kg) centreline bomb and two 110 lbs (40 kg) bombs or flares on under wing racks.

Bloch M.B.175 T - With a good survival rate, many aircraft survived the war and were adopted to the torpedo carrying role with the French Aéronavale until withdrawn from service in 1950. 

Specifications (Bloch M.B.174 A.3)

Type: Three Seat Reconnaissance & Light Bomber

Design: Henri Deplante Chief Designer at Bloch

Manufacturer: SNCASO

Powerplant: (M.B.170.01) Two 950 hp (708 kW) Gnome-Rhône 14N-6/7 radial engines. (M.B.170.02) Two 1,030 hp (768 kW) Gnome-Rhône 14N-20/21 14-cylinder radial engines. (M.B.174 A.3) Two 1,100 hp (820 kW) Gnome-Rhône 14N-48/49 14-cylinder radial engines.

Performance: Maximum speed 329 mph (530 km/h) at 17,060 ft (5200 m); cruising speed 248 mph (400 km/h); service ceiling 36,090 ft (11000 m); climb to 26,250 (8000 m) in 11 minutes.

Range: Maximum range 1,025 miles (1650 km) on internal fuel. Range with 882 lbs (400 kg) bombload 802 miles (1290 km).

Weight: (M.B.174 A.3) Empty 12,346 lbs (5600 kg) with a maximum take-off weight of 15,784 lbs (7160 kg). (M.B.175 B.3) Empty 12,480 lbs (5660 kg) with a maximum take-off weight of 17,690 lbs (8023 kg).

Dimensions: Span 58 ft 8 3/4 in (17.90 m); length 40 ft 2 1/4 in (12.25 m); height 11 ft 7 3/4 in (3.55 m); wing area 409.03 sq ft
(38.00 sq m).

Armament: (M.B.174 A.3) Two forward firing 7.5 mm (0.295 in) MAC 1934 machine-guns in the wings, two 7.5 mm (0.295 in) MAC 1934 machine-guns in the dorsal position and three 7.5 mm (0.295 in) MAC 1934 machine-guns on aft-firing wobble mounts plus a maximum bombload of up to 882 lbs (400 kg) usually consisting of eight 110 lbs (40 kg) bombs. Underwing racks could be added to carry light bombs or flares. In 1942 surviving aircraft were modified to carry a single 1,102 lbs (500 kg) bomb for shallow dive bombing. (M.B.175 B.3) Bombload was increased to 1,323 lbs (600kg) usually consisting of three 441 lbs (200 kg) or a single 1,102 lbs (500 kg) centerline bomb and two 110 lbs (40 kg) bombs on underwing racks. (M.B.175 T) Carried a single torpedo.

Variants: M.B.170.01 (prototype), M.B.170.02, M.B.174.01 (prototype), M.B.174 A.3, M.B.175 B.3 (light bomber), M.B.175 T (torpedo).

Avionics: None.

History: First flight (M.B.170.01) 15 February 1938; first flight (M.B.174.01) 5 January 1939; production (M.B.174 A.3) 5 November 1939; first delivery (M.B.174 A.3 to GR II/33) 19 March 1940; first operational sortie (M.B.174 A.3) 29 March 1940.

Operators: France (Armée de l'Air, Aéronavale, Vichy Air Force), Germany (Luftwaffe).