The JB-2 Loon, an American copy of the German V1 Flying Bomb, was the first American guided missile and was intended for the invasion of Japan. The first JB-2 was launched in October 1944, but the war ended before it could be used against the enemy. It was launched from a 175 long ramp elevated to 6 degrees, using either a fuel-powered catapult or a rocket powered launcher, and it could also be mounted on a solid-fueled rocket sled that quickly boosted its speed to 250 mph, allowing launch from a very short platform such as the deck of a submarine. Powered by a pulse jet engine burning gasoline, it reached speeds of 440 mph. Its guidance was controlled by a gyroscope, monitored by a magnetic compass to maintain a fixed heading, while an altitude control and air-log measured distance traveled; when the air-log reached its prescribed setting, the arming circuit closed and the controls locked into a dive position, causing the missile to plunge to its target. The Loon was accurate within a quarter of a mile at a range of 100 miles, and its specifications were length 27 ft 1 in., weight 5,025 lbs., range 150 miles, and a warhead of 200 lbs. of high explosive.