This is why Bunker Buster bombs are made from spent howitzer barrels

It was a common sight during Desert Storm: grainy black-and-white footage of an Iraqi bunker or hanger slowly getting closer and closer to the screen.

Munitions with cameras fed the footage of new, precision-guided "smart bombs" to Americans watching the war at home.

Saddam Hussein's Iraqi Army used underground facilities beneath layers of sand and reinforced concrete to protect his command and control centers, research labs, and ammo dumps. The U.S. military tasked its defense apparatus to come up with a way to penetrate and destroy these shelters.

Thus, the GBU-28 Bunker Buster bomb was born.

The GBU-28 is a 4,400-pound monster of hardened steel and tritonal explosives, a mixture of TNT and aluminum powder. Once the target is marked with a laser, that laser guides the bomb to its target and the rest (like the target) is history.

That hardened steel is what protects the bombs for their initial penetration through concrete. Barrels of artillery guns are designed to hold up to repeated artillery blasts, which is why the U.S. Army Watervliet Arsenal used barrels from 8-inch self-propelled howitzers as casings for the design.

That protection the spent barrels provide is perfect to give the bunker buster bomb time to penetrate a target while its time-delay fuse waits to unleash the real payload.

Engineering changes to the initial casing were made via telephone, even as the original barrels were being stripped and reconfigured by machinists on the assembly line. Watch the whole story of the birth of the bunker buster bomb in the video below.