Abstract: A vehicle launch assembly for underwater platforms includes a water tank mounted on the platform, and a plunger movably disposed in the tank and dividing the tank into first and second zones, the first zone being in communication with a. water environment in which the platform is disposed, and the second zone being in communication with a launch tube inlet line mounted on the platform. An actuator is connected to the plunger and is operable to move the plunger in the tank. A triggering device initiates operation of the actuator, moving the plunger in the tank to push water from the tank second zone to the launch tube inlet line to eject a vehicle from the launch tube, or moving the plunger to enlarge the tank second zone to draw water thereinto from a valve in communication with the water environment and the tank.