French engineer who with Jacques-Yves Cousteau designed the Self-Contained Underwater Breathing Appartus, also known as the aqualung. In 1943 Cousteau and Gagnan developed the aqualung tank that released compressed air activated by the breath itself. Gagnan perfected the regulator valve that would automatically feed the compressed air to the mouthpiece in ratio to the diver's breath. This invention allowed for the exploration of the ocean depths for scientific observation, military use, and recreational purposes.