Why was the aqualung invented?

Two French men, Jacques-Yves Cousteau (June 10, 1910-June 25, 1997) and Emile Gagnan (November 1900-1979) invented the Aqualung in 1943. It was the first open-circuit free-swimming underwater breathing set.

Jacques Cousteau amd Emile Gagnan.
It was invented in 1943 by Jacques Yves Cousteau and Emil Gagnan. Wikipedia has a detailed page on the subject - see related link.