a hole where a safety pin kept the sensor from being depressed. This pin was removed once the mine was planted. If the discovered mine was fitted with the pressure sensor, the disarming personnel would slip a pin (such as a sewing needle or pin) into this hole. If the device was armed with a tripwire or electrical trigger, this could simply be cut. Germans were known to use booby traps to discourage this, so caution was suggested. The mine could then be removed carefully from the ground and the sensor easily unscrewed. If it was deemed necessary to render the mine completely inert, three plugs on the top granted access to the three detonators inside the mine. These could be unscrewed and the detonators removed. Internal components The following diagrams show the SMi-35 mine's internal mechanism, together with the three-pronged pressure fuse. The safety pin for the fuse and the three removable plugs for the detonators are clearly visible. These diagrams were issued as part of a US Army field manual on mines in 1943. Imitations The S-mine was an extremely successful design. Bounding mines based on its design were introduced by other countries. The Finnish army began purchasing the SMi-35 model S-mine from Germany following the Winter War. This was part of a larger military assistance agreement between the two nations. Finnish forces experienced great success with the S-mine, but its monetary cost was considerable. During the Continuation War, the Finns unsuccessfully attempted to produce their own version of the mine. The Finnish nickname for the mine was Hyppy-Heikki ("Hopping Henry"). The French Mle 1939 mine was inspired by the success of the S-mine. In 1940, Major Paul Delalande of the French Corps of Engineers managed to escape the German conquest of his country and reached the United States with the Mle-1939 plans. These plans led to the development of the American M2 mine, which was fielded in 1942 but proved deficient in combat. The American army was impressed by the S-mine's role in thwarting the French offensive in the German Saar region at the beginning of World War II and continued further work on bounding mines. After the war, the American army developed their M16 mine directly from captured S-mine designs. The Soviet Union also based the design of its OZM series of mines on the German S-mine. Soviet mines tended to be far simpler internally; instead