"Union" was a trade name used by French and Spanish arms manufacturers (as well as American, actually) - but this particular Union is a French example. Among their many variations of pistols available (25, 32, long, short, extended barrels, etc) was a fully automatic version. For that pistol, they also developed a 35-round "horseshoe" magazine to provide maximum capacity without overly hampering the gun's handling. These are extremely rare today, as not many were initially manufactured.