The Washington Naval Treaty had placed strict limits on naval construction by the major naval powers, but submarines had been omitted. The French Navy attempted to take advantage of this by building three "corsair submarines", of which Surcouf was the only one to have been completed. Surcouf also carried a motorboat, and contained a cargo compartment with fittings to restrain 40 prisoners. The submarine's fuel tanks were very large; enough fuel for a range and supplies for 90-day patrols could be carried.