Probably more powerful than similareraft used by foreign navies, the newest type United States torpedo_boat, the PT-6, has a theoretical topspeed rating of sixty miles an hour. In the first tests, which were made before its three 1,250-horsepower motors had been broken in, the off-shore defender thundered over a lake at forty-six miles an hour, with no attempt to reach its limit. Manned by a crew of ten, the eighty-one foot boat has a cruising range of 2,000 miles. It is armed with torpedo tubes, depth charges and machine guns, and a single fighting unit costs. $218,000.