The mine detector (Polish) Mark 1 was a metal detector used to locate landmines. It was developed during World War II in the winter of 1941/1942 by Polish lieutenant Józef Kosacki.[1]​.

In the run-up to the war, the Artillery Department of the Polish Ministry of National Defense ordered the construction of a device that could be useful in locating unexploded ordnance at artillery training ranges.

The instrument was designed by the electronic company AVA Radio Company"), but its execution was prevented by the outbreak of the Polish defensive war. After the invasion of Poland in 1939 and the transfer of the Polish government to France, work restarted on the device, this time conceived as a mine detector. Little is known about this stage of construction, as work was stopped by the Battle of France and the need to evacuate personnel from Poland to Great Britain.

There, at the end of 1941, Lieutenant Józef Kosacki came up with a final project, based in part on the first designs. His discovery was not patented, he gave it as a gift to the British army. He received 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 rate of advance of the British 8th Army. During the war more than 100,000 detectors of this class were produced, along with several hundred thousand of the new mine detector developments (Mark II, Mk. III and Mk IV). The detector was later used during the Allied invasion of Sicily, the Allied invasion of Italy and the invasion of Normandy. This type of detector (Mark 4c) was used by the British Army until 1995.

"The Polish detector had two coils, one of which was connected to an oscillator that generated an oscillating current with an acoustic frequency. The other coil was connected to an amplifier and a telephone. When the coils were in proximity to a metal object, the balance between the coils was interfered with and the telephone communicated a signal. The equipment weighed just under 30 pounds (14 kg) and could be operated by a single man. The Polish detector was in service throughout the war and the Mark 4c version It was still used by the British Army until 1995.".

—Mike Croll, The History of Landmines.