Abstract: There is described a wet back device for generating waves in a liquid in a test tank or the like. Such devices are known and usually operate a wave generating board by a push-pull piston operation or a flapping wave generating board pivoted in the tank and rocked about a horizontal axis to move water in the tank and create waves therein. The device described is capable of producing the push-pull generated wave motion or the flapper type motion, or a combination of those motions and is provided with seals between the wave generating board and the tank walls or between individual wave generating boards (in a multiple board arrangement) and the walls of the tank. Closure plates are provided on the support frames for the boards. Gliding surfaces are provided to ensure reliable action and frame members are located to provide energy loss in fast flowing water in the tank.