Surcouf was a large French gun-armed cruiser submarine of the mid 20th century. She carried two 8" guns as well as anti-aircraft guns and (for most of her career) a floatplane. Surcouf served in the French Navy and, later, the Free French Naval Forces during the Second World War.
Surcouf disappeared during the night of 18/19 February 1942 in the Caribbean Sea, possibly after colliding with the US freighter Thompson Lykes, although this is not definitely established. She was named after the French privateer and shipowner Robert Surcouf. She was the largest submarine built until surpassed by the first Japanese I-400 class aircraft carrier submarine in 1944.
Type: Cruiser submarine
Beam: 9m (29 ft 6 in)
Draft: 7.25 m (23 ft 9 in)
Test depth: 80 m (260 ft)
Boats & landing craft carried:
Complement: 8 officers and 110 men
Aviation facilities: Hangar
A Unique Design
The Washington Naval Treaty had placed strict limits on naval construction by the major naval powers in regard to displacements and artillery calibers of battleships and cruisers. However, no agreements were reached in respect of light ships such as frigates, destroyers or submarines. In addition, to ensure the country's protection and that of the empire, France mounted the construction of an important submarine fleet (79 units in 1939). Surcouf was intended to be the first of a class of three submarine cruisers; however, she was the only one completed.
The missions revolved around the following:
The boat was equipped with ten torpedo tubes: four 550 mm (22 in) tubes in the bow, and two swiveling external launchers in the aft superstructure, each with one 550mm and two 400 mm (16 in) torpedo tubes. Eight 550mm and four 400mm reloads were carried.
The 203mm/50 Modèle 1924 guns were in a pressure-tight turret forward of the conning tower. The guns had a 60-round magazine capacity and were controlled by a director with a 5 m (16 ft) rangefinder, mounted high enough to view an 11 km (5.9 nmi; 6.8 mi) horizon, and able to fire within three minutes after surfacing. Using the boat's periscopes to direct the fire of the main guns, Surcouf could increase the visible range to 16 km (8.6 nmi; 9.9 mi); originally an elevating platform was supposed to lift lookouts 15 m (49 ft) high, but this design was abandoned quickly due to the effect of roll. The Besson observation plane could be used to direct fire out to the guns' 26 mi (23 nmi; 42 km) maximum range. Anti-aircraft cannon and machine guns were mounted on the top of the hangar.
Surcouf also carried a 4.5 m (14 ft 9 in) motorboat, and contained a cargo compartment with fittings to restrain 40 prisoners or lodge 40 passengers. The submarine's fuel tanks were very large; enough fuel for a 10,000 nmi (19,000 km; 12,000 mi) range and supplies for 90-day patrols could be carried.
The test depth was 80 m (260 ft).
The first commanding officer was Frigate Captain (Capitaine de Frégate, a rank equivalent to Commander) Raymond de Belot.
The boat encountered several technical challenges, owing to the 203mm guns.