Assembly and method for determining speed of a supercavitating underwater vehicle

An assembly for determining the speed of a supercavitating underwater vehicle during underwater travel, the assembly comprising:

• a fin mounted on the supercavitating underwater vehicle aft of a cavitator portion of the supercavitating underwater vehicle and adapted to be extended outwardly beyond a hull of the supercavitating underwater vehicle and through a boundary of a gas-filled cavity around the supercavitating underwater vehicle to form a disturbance in the cavity boundary, which disturbance propagates along the boundary;
• an acoustic transmitter mounted on the supercavitating underwater vehicle for directing acoustic energy toward the boundary and the disturbance;
• an acoustic receiver mounted on the supercavitating vehicle at a known distance from the acoustic transmitter for receiving acoustic energy reflected off of the disturbance;
• and
• an autopilot mounted on the supercavitating underwater vehicle for recording times of projection of said fin and for recording times of receptions of reflected acoustic energy to determine the speed of the supercavitating vehicle through the water.