A down-the-hole drill (DHD) hammer having a casing, a drill bit proximate a distal end of the casing, a piston mounted within the casing and a self-indexing drive transmission is provided. The piston includes a plurality of helical and axial splines. The drive transmission includes a driver sleeve, a driven sleeve and a wrap spring clutch assembly. The driver sleeve and driven sleeve are housed within the casing and circumscribes the piston. The driver sleeve includes a plurality of openings for receiving a plurality of bearings. The driver sleeve bearings are configured to operatively engage the helical splines on the piston. The wrap spring clutch assembly includes a wrap spring circumscribing the driver sleeve and driven sleeve. The driven sleeve operatively engages the drill bit to rotationally index the drill bit.