There in late 1941 Lieutenant Józef Kosacki devised a final version, based partially on the earlier designs. His invention was not patented; he gave it as a gift to the British Army. He was given a letter of thanks from the King for this act. His design was accepted and 500 mine detectors were immediately sent to El Alamein where they doubled the speed of the British Eighth Army. During the war more than 100,000 of this type were produced, together with several hundred thousands of further developments of the mine detector (Mk. II, Mk. III and Mk IV). The detector was used later during the Allied invasion of Sicily, the Allied invasion of Italy and the Invasion of Normandy. This type of detector was used by the British Army until 1995.