This how the Army introduced the plastic explosive in the 1960s

Today, plastic explosives are a given. But 50 years ago, they were the latest in demolition technology. One of the most notable, of course, is C4.

Officially, it is called the M118 demolition charge, and was called Flex-X back then. Prior to the introduction of Flex-X, explosives had to be secured to what the engineers wanted to blow up.

C4, though, was more like Play-Doh or used chewing gum in that it could be stuck to whatever needs to go away.

explosive

Composition C-4 demolition charges await use as explosive ordnance disposal technicians conduct demolition operations supervisor training. (U.S. Navy photo by Chief Mass Communication Specialist Kathryn Whittenberger)

The explosive had some other advantages as well. It could be used underwater, which means that divers could plant it on a pier without having to surface and risk being seen.

The explosive was also very insensitive. The video below shows troops dropping a weight on the Flex-X to no effect. It wouldn’t even go off when shot by multiple rounds from a M14 service rifle or when tossed into a campfire.

Those two shots from a M14 rifle did not set off the M118 charge. The third wasn’t the charm, either. (Youtube screenshot)

It also took much less time to set up – almost 60 percent less – when compared to earlier explosives, thanks to that Play-Doh/chewing gum consistency. That would save the lives of the engineers, who would spend less time away from cover.

Cold weather had little effect on the explosive’s ability to stick to whatever needed to be blown up. Other explosives needed to be taped or otherwise secured to the target.

According to the Federation of American Scientists, the M118 came in a box of 20 charges, each of which had four eight-ounce sheets of C4. A sales sheet from one manufacturer notes that the M118 is intended for breaching, ordnance disposal, demolition, and cutting metal.

The explosive replaced stocks of TNT, dynamite, and PETN in U.S. military stockpiles.