A two-inch pothole will give most family cars a bad jolt. Imagine what a 200-foot atomic bomb crater might do.

That’s not a problem most of us encounter on our morning commutes. But it is something that the U.S. military had no choice but to ponder. During the Cold War, America placed Atomic Demolition Munitions—nuclear land mines—on the West German and Italian borders and also along the Korean Demilitarized Zone.

The bombs were buried along key invasion routes and transportation bottlenecks, such as bridges and mountain passes. If the Soviets or North Koreans had attacked, the Americans would have detonated the ADMs, creating obstacles of rocks, downed trees, radiation—and whopping big craters.

If the nuclear land mines weren’t enough, there were also Special Forces teams that could parachute behind enemy lines carrying backpack-size nukes.

While plotting this atomic destruction, someone finally asked the hundred-kiloton question. Would these giant potholes actually be big enough to block Soviet tanks? Or could an armored vehicle just clank down, through and up the other side?

The Army decided to find out. In 1969 the ground combat branch conducted Project Tank Trap, an unimaginatively named program that drove tanks into giant craters.

“Project Tank Trap was conducted to determine the capability of selected tactical vehicles to traverse craters typical of those which could be produced with Atomic Demolition Munitions,” states the subsequent Army report.

The tests took place at the then-Atomic Energy Agency’s nuclear bomb test range in Nevada. The test range was the site of more than a thousand nuclear explosions during the Cold War, so the government had no problem finding suitable craters.

The research focused on three craters. The Pre-Schooner Bravo crater, 25 feet deep and 49 feet wide, represented atomic demolitions in hard rock.

The Scooter crater, 75 feet deep with a radius of 155 feet, simulated a nuclear crater in loose, dry soil.

Jangle-U, 55 feet deep and with a radius of 136 feet, also represented a demolition in dry soil, although at a shallower depth than Scooter. While the other two craters had been formed by detonating hundreds of tons of high explosives, a real atomic bomb—a 1.2-kiloton device buried 17 feet down—created Jangle-U.

The test vehicles were the M-60 tank, the M-113 armored personnel carrier and an articulated, two-piece light vehicle called the Polecat.

In some cases, the heavier armored vehicles had to be winched down and up the steep crater walls by a recovery vehicle. On one occasion, the winch failed. “The M-60 freewheeled into the crater from just above the half way point,” the report recalls. “The vehicle crossed the crater bottom to the opposite slope and rolled back to rest on the bottom. There was no apparent damage to the vehicle.”

Can you guess which vehicle performed best? Although tracked armored vehicles are supposed to have the best all-terrain mobility, it was the Polecat rather than the armored behemoths that was most successful negotiating the dry alluvial soils at Scooter and Jangle-U. This was because the articulated utility vehicle exerted less ground pressure at its rear.

The Army discovered that atomic demolitions in dry soil, and at shallow depth, would not block tanks. The crater slopes were too shallow and flat. But bury the ADM 160 feet down, and the crater became an obstacle.

However, it turned out that the best way to stop tanks was a nuclear explosion on hard rock. Not so much because of the crater itself, but rather due to the large number of rocks strewn around, which blocked vehicle movement.

Of course, one wonders whether the real obstacle would have been a Soviet tank commander having second thoughts about driving into a big hole that glowed in the dark.

This article first appeared at War is Boring.

Image: Wikipedia.