Compared to the Type XXI, the Narval class introduced an entirely new schnorchel system and novel detection systems, gained 33% in operational range on electric power (400 nautical miles (740 km; 460 mi), compared to the 290 nmi (540 km; 330 mi) available to the type XXI), and doubled the test depth.

From 1966 to 1970, the Narvals underwent extensive modernisation, where their engines were replaced by a diesel-electrical design based on the SEMT-Pielstick 12PA4-185.

In 1964, Espadon and Marsouin sailed up to the 70th parallel north to prepare the first French attempts at navigation under sea ice.

These tests were carried out the next year by Dauphin and Narval when they spent a week and a half in the 72nd parallel north.

Similarly, Dauphin was extensively modified from 1986 to be used as a test bed for equipment and sensors to be installed on the Triomphant-class submarines, then under design.