What you need to know about the 'mother of all bombs' The bomb is one of the largest in the U.S. arsenal.

 -- The U.S. military on Thursday dropped an MOAB, an approximately 22,000-pound bomb nicknamed the "mother of all bombs," on ISIS forces in Afghanistan — the first time it has been used in combat.

The bomb is touted as one of the largest non-nuclear weapons in the U.S. military's arsenal. Here's what you need to know:

What is the MOAB? When was it developed?

"MOAB" doesn't actually stand for "mother of all bombs"; its formal name is the GBU-43/B Massive Ordnance Air Blast.

The U.S. military developed the bomb in 2003, and at the time, "the goal was to put pressure on then-Iraqi dictator Saddam Hussein to cease and desist United Nations violations," according to the Air Force's website.

According to Chris Harmer at the Institute for the Study of War, it has a "blast equivalent of 11 tons of TNT."

The Air Force Research Laboratory Munitions Directorate at Eglin Air Force Base near Valparaiso, Florida, developed the bomb, which uses GPS to navigate to its target, according to the Air Force.

The bomb is so large that it is carried in the cargo hold of an MC-130 aircraft before it is extracted by parachute from the rear of the plane, Air Force spokeswoman Ann Stefanek said.

"The MOAB then releases from the cradle within 5 seconds of extraction and utilizes global-positioning-satellite-aided guidance and controllable fins to maneuver accurately — to within less than 8 meters — of the intended impact point," she said.

Why was it used in Afghanistan?

The bomb was used against ISIS-Khorasan (ISIS-K) fighters in eastern Afghanistan on Thursday around 7:30 p.m. local time (around 10:30 a.m. ET).

The target was an ISIS-K tunnel complex in the Achin district of the Nangarhar province in Afghanistan.

ISIS-K has been "using IEDs, bunkers and tunnels to thicken their defense" as its "losses have mounted," said Gen. John Nicholson, the commander of U.S. Forces – Afghanistan.

According to Harmer, the use of the bomb could indicate that the U.S. does "not have the depth of resources in Afghanistan to fight effectively against the Taliban/AQD/ISIS" and is "resorting to the MOAB out of desperation."

"The trend over the last 15 years has been to go smaller and more accurate with our weapons," he said.

He said that its use may also be "a signal to [North Korean] leadership that the U.S. has massive conventional weapons that could theoretically be used in a first-strike situation against their nuclear weapons and delivery program."

The MOAB, however, "is not a penetrator weapon and is primarily intended for soft to medium surface targets covering extended areas, targets contained in an environment such as caves or canyons, clearing extensive minefields and for psychological effects," Stefanek said.

Had it been used before?

The MOAB had not been used in combat until Thursday.

The bomb was first tested on March 11, 2003, according to the Air Force.

Who authorized use of the bomb in Afghanistan?

Nicholson had the authority to drop the bomb, U.S. officials said, but it's unclear what that authority entailed. Use of the bomb did not require presidential authority.

Asked Thursday if he authorized the strike, President Donald Trump said he authorized the military.

"Everybody knows exactly what happened, and what I do is I authorize my military … We've given them total authorization," he said.

He added, "Frankly, that's why they've been so successful lately," saying recent weeks stand in contrast to the last eight years under President Barack Obama.

According to officials, the bomb had been in Afghanistan since the fall of 2016, during the Obama administration.

How does it compare with other bombs?

The bomb is among the largest non-nuclear weapons in the U.S. military's arsenal.

The largest non-nuclear bomb is the massive ordnance penetrator (MOP), which weighs in at about 30,000 pounds and has never been used in combat.

The MOAB has other competition on the world stage.

According to a 2007 article in The Guardian, Russia claimed to have developed the "father of all bombs," which it says is four times as powerful as the MOAB.

ABC News' Luis Martinez contributed to this report from the Pentagon.