In a submarine countermeasure vehicle and launch assembly the vehicle includes a forward end portion, an aft end portion provided with a propeller and fins, a hull portion extending between the forward and aft portions, the hull portion being circular in cross-section, and a thrust ring mounted on the fins and around the propeller, the thrust ring forming a convex configuration. The launch assembly includes a launch tube for retaining and launching the vehicle, a ram plate moveable in the launch tube to push the vehicle out an end of the launch tube, the ram plate having an engagement surface for contact with the thrust ring, the engagement surface being at least in part of a concave configuration. In a launch operation, the concave surface of the ram plate engages the convex configuration of the thrust ring.