Here is the patent diagram for an impressive band gun devised by Commander Yves Le Prieur who was a diving pioneer, prolific inventor and Navy man and should be as well-known as Captain Jacques Cousteau. Among his many achievements are the first practical scuba, the first underwater “Nautilus” speargun powered by blank cartridges and later by bottled compressed air and the formation of the world’s first diving club using his “Scaphandre” breathing apparatus. Alexandre Kramarenko patented the world's first underwater spring powered speargun in 1937, but hot on its heels was this much more practical and floating band gun which was patented, in terms of its priority date, in December 1938.
Unlike many subsequent speargun patents in the thirties and forties this gun actually worked. Note the provision of front and rear targeting sights on the speargun and the eight band power system which even with the relatively weak rubber of the time would have delivered a powerful shot. A floating reel is used with the gun and there is an optional shoulder stock which is similar to the one on the “Nautilus” cartridge/compressed air speargun. A leaf spring item 28 on the patent diagram stops the spear falling out of the gun's side-slotted barrel tube by pressing upwards against the tail end of the spear. The spear has a replaceable tip and a pivoting flopper located behind the spear tip to retain the speared fish, so everything required to successfully spear fish underwater is in place 80 years ago!
The "Nautilus" gun in its cartridge powered form, being demonstrated by Commander Le Prieur, is shown in the attached photo.