From George G. Blackburn's Where The Hell Are The Guns?:
The buzz-bomb menace, which, for several weeks at the beginning, seriously reduced production of goods and services vital to the prosecution of the war (according to the diary notes of the Chief of the Imperial General Staff, General Alan Brooke) was brought under control by the timely arrival on the ack-ack (anti-aircraft) gunnery scene of the proximity fuse - a Canadian-American invention based on a British idea. Shells from the 3.7-inch ack-ack guns, which would have sailed past a few feet from a buzz bomb, were caused to burst and send lethal fragments into the buzz bombs' vitals when a tiny radio-transmitter bounced back from the pilotless monster.
The Americans developed the tiny radio transmitter and receiver. Canada supplied the design for a dependable power supply, which had to have long storage life but produce instant power to the little radio transmitter as the shell left the gun. Regular tiny batteries, with their limited shelf life, were useless, but scientists at the National Research Council in Ottawa, working with industrial scientists in Toronto, produced the answer: a battery that would remain dormant until activated by acid from a tiny vial broken within the fuse by the shocking wham of the propellant charge sending the shell on its way.1
http://www.canadiansoldiers.com/weapons/ammunition/proximityfuze.htm