In 1934 Le Prieur was granted French patent 768083 for an improved hand-controlled self-contained underwater breathing apparatus with full face mask. The patent application was lodged in Paris on 2 February 1934 at 2:32 pm. The patent was awarded on 7 May 1934 and the patent specification was published on 31 July 1934. The equipment delivered air at constant pressure without a demand regulator. Compressed air was contained in a cylinder carried on the diver's chest in a harness, delivering air to the full face mask at a pressure controlled by a hand-operated regulator. Excess air, and the diver's exhaled breath, escaped by slightly lifting the edges of the mask.