The U.S. Air Force dropped the the second largest conventional bomb in its arsenal, and the largest conventional bomb to be used in combat, on ISIS forces in Afghanistan today. Thirty feet long and weighing as much as a F-16 fighter, the GBU-43/B bomb—also known as Massive Ordnance Air Blast, MOAB, or "Mother Of All Bombs"—is designed to destroy enemy forces both in the open and in enclosed spaces.

The bomb was reportedly used on an Islamic State tunnel complex in Afghanistan's Nangarhar Province. A U.S. Air Force Special Operations Command MC-130 Combat Talon transport aircraft dropped the GPS-guided bomb out of the cargo ramp.

Here's a video of a past test:

The GPS-guided MOAB weighs 21,700 pounds and is filled with 18,700 pounds of H6 explosive . The thirty foot long aluminum casing weighs only 3,000 pounds, which is an unusually low proportion of the bomb's overall weight. Unlike many bombs, for which steel shrapnel is a primary effect, the MOAB is designed to generate explosive shockwaves and is stuffed as full of as much explosive as possible. A bomb that kills through overpressure, the MOAB is well suited for destroying cave complexes. Waves of pressure entering a cave system cause injuries and fatalities, and the shock can collapse earthen tunnels.

Technicians preparing for the first MOAB test, 2003.

U.S. Air Force photo.

The GBU-43/B was developed in-house by the Air Force Research Laboratory Munitions Directorate. It was first tested in March 2003 at Eglin Air Force Base in Florida, when it produced a mushroom cloud that could be seen up to 20 miles away.

Believe it or not the U.S. has a second, even larger bomb. The GB-57A/B Massive Ordnance Penetrator (MOP) GBU-57 A/B weighs 30,000 pounds and is designed to penetrate underground concrete structures.