without being used to destructive effect (e.g. shrapnel). Tellermine was the prototypical anti-tank mine, with many elements of its design emulated in the Pignone P-1, NR 25, and M6 mine (among others). Because of its rather high operating pressure, a vehicle would need to pass directly over top of the mine to set it off. But since the tracks represent only about 20% of a tank's width, the pressure fuse had a limited area of effect. As one source has it: "Since they were pressure-detonated, these early anti-tank mines typically did most of their damage to a tank's treads, leaving its crew unharmed and its guns still operational but immobilised and vulnerable to aircraft and enemy anti-tank weapons ... During World War II they (the Wehrmacht) began using a mine with a tilt-rod fuze, a thin rod standing approximately two feet up from the center of the charge and nearly impossible to see after the mine had been buried. As a tank passed over the mine, the rod was pushed forward, causing the charge to detonate directly beneath it. The blast often killed the crew and sometimes exploded onboard ammunition. Now that tank crews were directly at risk, they were less likely to plow through a minefield." Although other measures such as satchel charges, sticky bombs and bombs designed to magnetically adhere to tanks were developed, they do not fall within the category of land mines as they are not buried and detonated remotely or by pressure. The Hawkins mine was a British anti-tank device that could be employed as a mine laid on the road surface for a tank to run over setting off a crush fuze or thrown at the tank in which case a timer fuze was used. Shaped charge devices like the Hohl-Sprung mine 4672 were also developed by Germany later in the war, although these did not see widespread use. The most advanced German anti-tank mine of the war was their minimal metal Topfmine. In contrast to the dinner plate mines such as the German Tellermine were bar mines such as the German Riegel mine 43 and Italian B-2 mine. These were long mines designed to increase the probability of a vehicle triggering it, the B2 consisted of multiple small shaped-charge explosive charges along its length designed to ensure a mobility kill against enemy vehicles by destroying their tracks. This form of mine was the