The proximity fuze increased the lethality of antiaircraft guns in a way not possible even for well-laid, well-planned ground-based air defense networks. The proximity fuze made it possible, if not to always hit the target, to at least damage it with near-misses. The proximity fuze is a kind of miniature radar, designed to detonate its shell when a nearby object begins moving away. Prior to proximity fuzes the range to a target was estimated and, in the most advanced antiaircraft artillery pieces, automatically set in a mechanical fuze after being mathematically derived. The problem lay in the possible error in timing due to the erratic course of the target or a mistaken range reading, or even human error. The proximity fuze allowed the shell to detonate closer to the target than was possible except through sheer chance. Proximity fuzes were used with great success over England and arrived on the continent just in time to meet the threat posed by V-1s, the first cruise missiles. The jet-powered V-1 was a difficult target to hit, even with radar guidance of the guns. But proximity fuzes destroyed or critically damaged the majority of the "buzz bombs" well before they could hit London. Later in the war, U.S. antiaircraft gunners took advantage of the deadly fuze to shoot down most of the V-1s targeted against the vital Port of Antwerp.