The First Effective Mine Detector

Land mines have been around in one form or another for more than a thousand years. By now, you’d think a simple and safe way of locating and removing the devices would’ve been engineered. But that’s not the case. In fact, up until World War II, the most common method for finding the explosives was to prod the ground with a pointed stick or bayonet. The hockey-puck-size devices were buried about 15 centimeters below the ground. When someone stepped on the ground above or near the mine, their weight triggered a pressure sensor and caused the device to explode. So mine clearing was nearly as dangerous as just walking through a minefield unawares.

During World War II, land mines were widely used by both Axis and Allied forces and were responsible for the deaths of 375,000 soldiers, according to the Warfare History Network.

In 1941 Józef Stanislaw Kosacki, a Polish signals officer who had escaped to the United Kingdom, developed the first portable device to effectively detect a land mine without inadvertently triggering it. It proved to be twice as fast as previous mine-detection methods, and was soon in wide use by the British and their allies.

The Engineer Behind the Portable Mine Detector

Before inventing his mine detector, Kosacki worked as an engineer and had developed tools to detect explosives for the Polish Armed Forces.

After receiving a bachelor’s degree in electrical engineering from the Warsaw University of Technology in 1933, Kosacki completed his year-long mandatory service with the army. He then joined the National Telecommunications Institute in Warsaw as a manager. Then, as now, the agency led the country’s R&D in telecommunications and information technologies. In 1937 Kosacki was commissioned by the Polish Ministry of National Defence to develop a machine that could detect unexploded grenades and shells. He completed his machine, but it was never used in the field.

Polish engineer Józef Kosacki’s portable land-mine detector saved thousands of soldiers’ lives in World War II. Military Historical Office

When Germany invaded Poland in September 1939, Kosacki returned to active duty. Because of his background in electrical engineering, he was placed in a special communications unit that was responsible for the upkeep of the Warszawa II radio station. But that duty lasted only until the radio towers were destroyed by the German Army a month after the invasion.

With Warsaw under German occupation, Kosacki and his unit were captured and taken to an internment camp in Hungary. In December 1939, he escaped and eventually found his way to the United Kingdom. There he joined other Polish soldiers in the 1st Polish Army Corps, stationed in St. Andrews, Scotland. He trained soldiers in the use of wireless telegraphy to send messages in Morse code.

Then tragedy struck.

Tragedy Inspired Engineering Ingenuity

The invention of the portable mine detector came about after a terrible accident on the beaches of Dundee, Scotland. In 1940, the British Army, fearing a German invasion, buried thousands of land mines along the coast. But they didn’t notify their allies. Soldiers from the Polish 10th Armored Cavalry Brigade on a routine patrol of the beach were killed or injured when the land mines exploded.

This event prompted the British Army to launch a contest to develop an effective land-mine detector. Each entrant had to pass a simple test: Detect a handful of coins scattered on the beach.

Kosacki and his assistant spent three months refining Kosacki’s earlier grenade detector. During the competition, their new detector located all of the coins, beating the other six devices entered.

There’s some murkiness about the detector’s exact circuitry, as befits a technology developed under wartime security, but our best understanding is this: The tool consisted of a bamboo pole with an oval-shaped wooden panel at one end that held two coils—one transmitting and one receiving, according to a 2015 article in Aerospace Research in Bulgaria. The soldier held the detector by the pole and passed the wooden panel over the ground. A wooden backpack encased a battery unit, an acoustic-frequency oscillator, and an amplifier. The transmitting coil was connected to the oscillator, which generated current at an acoustic frequency, writes Mike Croll in his book The History of Landmines. The receiving coil was connected to the amplifier, which was then linked to a pair of headphones.

The detector weighed less than 14 kilograms and operated much like the metal detectors used by beachcombers today. Michał Bojara/National Museum of Technology in Warsaw

When the panel came close to a metallic object, the induction balance between the two coils was disturbed. Via the amplifier, the receiving coil sent an audio signal to the headphones, notifying the soldier of a potential land mine. The equipment weighed just under 14 kilograms and could be operated by one soldier, according to Croll.

Kosacki didn’t patent his technology and instead gave the British Army access to the device’s schematics. The only recognition he received at the time was a letter from King George VI thanking him for his service.

Detectors were quickly manufactured and shipped to North Africa, where German commander Erwin Rommel had ordered his troops to build a defensive network of land mines and barbed wire that he called the Devil’s Gardens. The minefields stretched from the Mediterranean in northern Egypt to the Qattara Depression in western Egypt and contained an estimated 16 million mines over 2,900 square kilometers.

Kosacki’s detectors were first used in the Second Battle of El Alamein, in Egypt, in October and November of 1942. British soldiers used the device to scour the minefield for explosives. Scorpion tanks followed the soldiers; heavy chains mounted on the front flailed the ground and exploded the mines as the tank moved forward. Kosacki’s mine detector doubled the speed at which such heavily mined areas could be cleared, from 100 to 200 square meters an hour. By the end of the war, his invention had saved thousands of lives.

Kosacki’s land-mine detector was first used in Egypt, to help clear a massive minefield laid by the Germans. The basic technology continued to be used until 1991.National Army Museum

The basic design with minor modifications continued to be used by Canada, the United Kingdom, and the United States until the end of the First Gulf War in 1991. By then, engineers had developed more sensitive portable detectors, as well as remote-controlled mine-clearing systems.

Kosacki wasn’t publicly recognized for his work until after World War II, to prevent retribution against his family in German-occupied Poland. When Kosacki returned to Poland after the war, he began teaching electrical engineering at the National Centre for Nuclear Research, in Otwock-Świerk. He was also a professor at what is now the Military University of Technology in Warsaw. He died in 1990. The prototype of Kosacki’s detector shown at top is housed at the museum of the Military Institute of Engineering Technology, in Wroclaw, Poland.

Land Mines Are Still a Worldwide Problem

Land-mine detection has still not been perfected, and the explosive devices are still a huge problem worldwide. On average, one person is killed or injured by land mines and other explosive ordnance every hour, according to UNICEF. Today, it’s estimated that 60 countries are still contaminated by mines and unexploded ordnance.

Although portable mine detectors continue to be used, drones have become another detection method. For example, they’ve been used in Ukraine by several humanitarian nonprofits, including the Norwegian People’s Aid and the HALO Trust.

Nonprofit APOPO is taking a different approach: training rats to sniff out explosives. The APOPO HeroRATs, as they are called, only detect the scent of explosives and ignore scrap metal, according to the organization. A single HeroRAT can search an area the size of a tennis court in 30 minutes, instead of the four days it would take a human to do so.

Part of a continuing series looking at historical artifacts that embrace the boundless potential of technology.

An abridged version of this article appears in the January 2025 print issue as “The First Land-Mine Detector That Actually Worked.”