Propelled on the surface by two diesel engines producing a combined 6,000 horsepower (4,474 kW), they had a maximum speed of 18.6 knots (34.4 km/h; 21.4 mph).

When submerged, their two electric motors produced a combined 2,250 horsepower (1,678 kW) and allowed them to reach 10 knots (19 km/h; 12 mph).

Also called "deep-cruising submarines", their range on the surface was 10,000 nautical miles (19,000 km; 12,000 mi) at 10 knots (19 km/h; 12 mph).

[3] Ouessant and the rest of the 8th Submarine Division next left European waters and proceeded to Fort-de-France on Martinique in the French West Indies to conduct patrols in the vicinity of Trinidad the British had requested.

[3] After a stop at Casablanca in French Morocco, the two submarines arrived at Brest on 1 February 1940 and began a major overhaul.

The Germans refloated Ouessant in 1942 to clear her berth and towed her to Bordeaux, France, where they hulked her for use as a floating power station.