France pursues an effective early submarine force

France's continuing search for an inexpensive answer to battleships helped drive its pursuit of an effective early submarine force. Submarines appeared cheap partly because they carried far fewer sailors than capital ships, making both the craft and their crews more readily expendable in contemporary calculations. Before sonar and mature depth charges, defenses relied heavily on ramming, minefields, hydrophones, and passive torpedo protection. Destroyers nevertheless began to acquire another role as submarine hunters, continuing the cycle in which a supposed offset weapon generated a countermeasure.