Science: The Bomb Tamer

At work excavating gravel from a water-filled pit in Kent, England last week, a workman felt his scoop hit an obstacle. He gave it an extra pull, and near fainted from fright: up came a 1,100-lb. bomb, a German dud from World War II. Within minutes, the Royal Engineers' Bomb Disposal Unit at Horsham, Sussex was racing to the rescue. A few hours later, all was clear again. The bomb was expertly defused and trucked off to a bomb graveyard where the explosive filling could be steamed out in safety —at least for Kent's homeowners.

That particular bomb was tame, but burly Major Arthur Hartley. 49, whose job since World War II has been to take the bang out of bombs, says that Britain's dud problem is getting worse instead of better. Of 505 unexploded bombs still on the Home Office charts, about 50% are considered "safe." But the rest range up to 4,600-lb. "Satans" equipped with multiple fuses of fiendish design—and the British are sure that there are hundreds more buried, unnoticed, deep in the soil. In many cases, the explosive is getting more sensitive as the years pass.

Tremblers & Traps. To stay ahead of the game, Britain's bomb men must call on a vast knowledge of chemistry, a store of cold nerve, and a touch as delicate as a Piccadilly pickpocket's. Hartley's first step is to chart the bomb's precise position by magnetic detectors that reveal the depth, how big the bomb is, how it lies. The trouble is that as bombs grow older, their metal tends to polarize with the earth, cancel out fine magnetic measurements. Hartley must know that a big, blocky bomb like the 4,000-lb. Satan may wind up nose down at a depth of 60 ft., while a smaller, more rounded "Hermann" (named for Goring) usually lies at 20 ft. or less, and nose up because of a retarder ring around its nose.

Finding the bomb is the least of it. Most German bombs had an electric fuse charged by current flowing through a long telescopic arm at the moment of release. When the bomb hit the ground, the shock worked a "trembler switch" that touched off the bomb's main charge. After 14 years, these electric fuses are dead, but what about the clockwork fuses used to back them up? Answer: a magnetic clock-stopper to freeze the mechanism.

The Germans were also very nasty about anti-handling booby traps. One type of fuse was supersensitized after the bomb hit the ground, with a switch so delicate that it could operate if the bomb shell was tapped with a pencil. Hartley's men learned to outwit some mechanisms by injecting a quick-setting plastic. If the bomb is too difficult to defuse, they drill holes in its casing and melt out the explosive with live steam.