the radio would be switched on by the vane counter, and a aerial deployed. A coded Morse signal, unique to each V1 site, transmitted the route, and impact zone calculated once the radio stopped transmitting. An odometer driven by a vane anemometer on the nose determined when the target area had been reached, accurate enough for area bombing. Before launch, it was set to count backwards from a value that would reach zero upon arrival at the target in the prevailing wind conditions. As the missile flew, the airflow turned the propeller, and every 30 rotations of the propeller counted down one number on the odometer. This odometer triggered the arming of the warhead after about . When the count reached zero, two detonating bolts were fired. Two spoilers on the elevator were released, the linkage between the elevator and servo was jammed, and a guillotine device cut off the control hoses to the rudder servo, setting the rudder in neutral. These actions put the V-1 into a steep dive.. While this was originally intended to be a power dive, in practice the dive caused the fuel flow to cease, which stopped the engine. The sudden silence after the buzzing alerted listeners of the impending impact. Initially, V-1s landed within a circle in diameter, but by the end of the war, accuracy had been improved to about , which was comparable to the V-2 rocket. Warhead The warhead consisted of 850 kg of Amatol, 52A+ high-grade blast-effective explosive with three fuses. An electrical fuse could be triggered by nose or belly impact. Another fuse was a slow-acting mechanical fuse allowing deeper penetration into the ground, regardless of the altitude. The third fuse was a delayed action fuse, set to go off two hours after launch. The purpose of the third fuse was to avoid the risk of this secret weapon being examined by the British. Its time delay was too short to be a useful booby trap, but was instead meant to destroy the weapon if a soft landing had not triggered the impact fuses. These fusing systems were very reliable, and almost no dud V-1s were recovered. Walter catapult Ground-launched V-1s were propelled up an inclined launch ramp by an apparatus known as a ("steam generator"), in which steam was generated when hydrogen peroxide (T-Stoff) was mixed with sodium permanganate (Z-Stoff). Designed by Hellmuth Walter Kommanditgesellschaft, the WR 2.3