MK. III "Polish" Mine Detector

Polish officer, Lieutenant Jozef Stanislaw Kozacki, invented the first practical electronic mine detector during World War II. In the winter of 1941-42, the British War Office invited designs for a robust and reliable mine detector. The one War Office adopted was submitted anonymously by Lieut. Jozef Stanislaw Kozacki, a signals officer with the 1st Polish Army Corps stationed in Scotland following the German defeat of  Poland in 1939. His invention was tested and developed and 500 Mine  Detectors No. 2 (Polish) were rushed to the Western Desert in time for the advance on El Alamein. Their effect was to double the speed of British troops that cleared the heavily mined sands from 100 to 200 meters an hour. His discovery was not patented; he gave it as a gift to the British Army (he was later given a thank you letter from the king). 

The same basic design continued in use for 50 years and last saw the action with British forces during the 1991 Gulf  War. 

From: "The History of Landmines" by Mike Croll published in Great Britain in 1998 by Leo Cooper, Pen & Sword Books Ltd. ISBN 0 85052 268 0, page 54:
 
"The mining of the beaches had several unexpected consequences. As the defense of Britain became more organized it became necessary to move or to re-lay minefields. The laying of the original fields was so poor that entirely new methods of clearance, laying and accurate recording had to be devised. The difficulties of locating buried mines in the shifting sands of the beach prompted the War Office to issue specifications for a mine detector during the winter of 1941/42. The design accepted was submitted by Lieutenant Jozef Stanislaw Kozacki, a Polish signals officer who had escaped to France and then to Britain in 1940. The Polish detector had two coils, one of which was connected to an oscillator which generated an oscillating current of an acoustic frequency. The other coil was connected to an amplifier and a telephone. When the coils came into proximity to a metallic object the balance between the coils was upset and the telephone reported a signal. The equipment weighed just under 30 pounds and could be operated by one man. The Polish detector saw service throughout the war and the Mark 4c version was still used by the British Army until 1995. The experience of mine warfare gained on the Home Front was to prove useful throughout the war. While the Germans dominated mine design and mine laying, the British were the great innovators in clearance techniques, initially as a result of their own shortsightedness."