Abstract: A reaction drive sprinkler including an improved drive nozzle assembly for rotating the sprinkler in steps about a water supply standpipe. The drive nozzle assembly comprises a fixed drive nozzle through which an inclined stream of irrigation water is projected for passage through a diverter tube mounted in front of the drive nozzle for movement between forward- and reverse-drive positions. The diverter tube is shifted between the forward- and reverse-drive positions by a spring-loaded, over-center reversing mechanism for slightly diverting the water stream for alternated interruption by a pair of laterally oppositely angled deflector spoons on a pivoting reaction drive arm.