For decades they have been an effective and lethal pair, the explosives behind so many of the military’s grenades, mortars and bombs. But TNT and Composition B can also be sensitive devils that detonate when they are not supposed to.

And that can have devastating effects.

A fire aboard the USS Forrestal set off a chain reaction of explosions that killed 134 sailors in 1967. In 1991, an ammunition carrier loaded with 155mm artillery shells caught fire at Camp Doha in Kuwait, setting off massive explosions that left three dead and dozens wounded.

But now the Army is involved in a massive effort that would eventually replace those weapons with what are called “insensitive munitions,” which are less susceptible to exploding inadvertently.

The technology, developed by BAE Systems, the large defense contractor, uses an explosive that is far more chemically stable and able to withstand extreme heat and outside interference, including getting hit by bullets or shrapnel.

TNT and Composition B “are generally stable,” said Mike Ervin, director of innovation and customer relations for BAE ordnance systems, and aren’t going to spontaneously explode. “But the issue with TNT and Comp B is shock sensitivity. Both are sensitive to external stimuli. If they get hit by a fragment or bullet, they could cause a chain reaction. And instead of losing one round, you could lose your whole store of ammunition.”

The Army is now using what’s called IMX-101 in some of their artillery, a far safer substance, officials say. And the service hopes to one day make all of its munitions “insensitive.” But that’s not going to happen quickly.

“It’ll definitely take a decade or two to turn over the entire inventory,” said Raymond Colon, project manager of the Army’s Combat Ammunition Systems.

The Army already claims at least one success involving the new technology. When a convoy carrying 60mm mortar rounds was hit by a bomb in Afghanistan a few years ago and caught fire, the shells didn’t explode. And that, officials said, saved lives.