What is the MOAB?

The Pentagon said Thursday that U.S. forces in Afghanistan dropped the military’s largest non-nuclear bomb on an Islamic State target in eastern Afghanistan. This is the first time a Massive Ordnance Air Blast bomb (MOAB) has been used in combat.

The Pentagon says the bomb was dropped on a cave complex believed to be used by ISIS fighters in the Achin district of Nangarhar province, very close to the Pakistan border.

Here’s what you need to know:

?   The MOAB, also known as the “Mother of All Bombs,” was dropped out of a C-130 aircraft in Afghanistan for the first time on Thursday.

?  The MOAB had never been used in combat until now. It was brought into service in 2008.

?  The MOAB weighs 21,000 pounds, including 18,000 pounds of explosives.

?  It is the largest non-nuclear weapon in the U.S. arsenal.

?  The MOAB is considered similar to a small nuclear weapon.

?  The concept behind the MOAB was first developed in the Vietnam War through the BLU-82B/C-130 weapon system, nicknamed the “Daisy Cutter.” That weighed 15,000 pounds and, with a huge blast radius, was used to clear jungles. In addition, it was a psychological weapon, in that the loud sound and huge flash helped create “shock and awe” in the enemy. The bomb was later used in Afghanistan.

?  During the George W. Bush administration, the BLU-82B gave way to the even larger GBU-43, or MOAB.

?  It was first tested back in 2003.

?  The bomb, in its first combat use, was dropped on an ISIS tunnel complex in Nangahar province. MOAB is designed for such a situation—it explodes in the air, which creates air pressure that can make tunnels and other structures collapse.  It can be used at the start of an offensive to soften up the enemy, weakening both its infrastructure and morale.

Fox News' Brooke Singman, Martin Hinton, Jennifer Griffin and Lucas Tomlinson contributed to this report.