The fascinating origin of the GBU-43 'mother of all bombs'

The 11-ton "mother of all bombs" dropped by U.S. forces on ISIS-linked fighters in Afghanistan is a highly specialized weapon with a heritage dating back to huge bombs developed for use against Nazi targets in World War Two.

The 21,600-pound (9,797-kg) GBU-43 (Guided Bomb Unit), one of only 15 ever built, was developed after the U.S. military found itself without the ordnance needed to deal with al Qaeda tunnel systems in the hunt for Osama Bin Laden in 2001.

But the Massive Ordnance Air Blast Bomb, or MOAB, as it is also known, had never been used in combat until a U.S. MC-130 aircraft dropped one on the Achin district of Nangarhar, bordering Pakistan, on Thursday.

Afghan officials say it killed as many as 36 suspected Islamic State militants, although a news agency affiliated with Islamic State in the Middle East carried a statement denying that the group had suffered casualties in the attack.

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The GBU-43/B Massive Ordnance Air Blast (MOAB) bomb is pictured in this undated handout photo. Elgin Air Force Base/Handout via Reuters
Smoke rises after an air strike on Islamic State (IS) militants positions during an ongoing operation against the group in the Achin district of Afghanistan's Nangarhar province on April 14, 2017, a day after the US military struck the district with its largest non-nuclear bomb. 
Afghan security forces take part in an ongoing operation against Islamic State (IS) militants in the Achin district of Afghanistan's Nangarhar province on April 14, 2017, a day after the US military struck the district with its largest non-nuclear bomb. 
Afghan security forces take part in an ongoing operation against Islamic State (IS) militants in the Achin district of Afghanistan's Nangarhar province on April 14, 2017, a day after the US military struck the district with its largest non-nuclear bomb. 
Afghan security forces take part in an ongoing operation against Islamic State (IS) militants in the Achin district of Afghanistan's Nangarhar province on April 14, 2017, a day after the US military struck the district with its largest non-nuclear bomb. 
Smoke rises after an air strike on Islamic State (IS) militants positions during an ongoing operation against the group in the Achin district of Afghanistan's Nangarhar province on April 14, 2017, a day after the US military struck the district with its largest non-nuclear bomb. 
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A U.S. official who monitored the attack said it was impossible to determine how many ISIS fighters might be buried in the underground complex. But he said it could be "significant" because the attack came at evening prayer time, when fighters might have been concentrated in one area.

The U.S. commander in Afghanistan said on Friday that the decision to use one of the biggest conventional bombs ever used in combat was purely tactical.

SEE ALSO: FOX News host: America's hitting ISIS with 'mother of all bombs' is 'what freedom looks like'

Experts said that while the use of the bomb was likely a technical decision of matching the most effective ordnance to a specific target - tunnels and caves in an unpopulated area - its shock waves would have been sent not only to ISIS fighters, but also to North Korea, which conceals its nuclear weapons program deep underground, and Iran, which has a large uranium enrichment facility buried in a granite mountain.

In addition, said an administration official who spoke on the condition of anonymity, the attack also reinforces the message that U.S. President Donald Trump has given his military commanders freer rein than did his predecessor, Barack Obama.

"What I do is I authorize my military," Trump told reporters on Thursday in response to a question about the use of the bomb. "We have the greatest military in the world, and they've done the job, as usual. We have given them total authorization, and that's what they're doing."

RELATED: The best military photos of 2016

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The best US military photos from 2016
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The best US military photos from 2016

An Air Force F-22 Raptor flies over the Arabian Sea to support Operation Inherent Resolve, January 27, 2016.

(Air Force photo by Staff Sgt. Corey Hook)

Marine Corps Sgt. Josh Greathouse scans the area during a perimeter patrol in Taqaddum, Iraq, March 21, 2016. Greathouse is a team leader assigned to Bravo Company, 1st Battalion, 7th Marine Regiment, Special Purpose Marine Air Ground Task Force Crisis Response, for US Central Command.

(Marine Corps photo by Sgt. Rick Hurtado)

Navy Seaman Fabian Soltero looks through shipboard binoculars aboard the aircraft carrier USS Dwight D. Eisenhower in the Atlantic Ocean, March 25, 2016.

(Navy photo by Petty Officer 3rd Class Taylor L. Jackson)

USS Bulkeley receives fuel and cargo from dry cargo/ammunition ship USNS Medgar Evers during a replenishment at sea in the Persian Gulf, February 25, 2016. The guided-missile destroyer was supporting Operation Inherent Resolve, maritime security operations, and theater security cooperation efforts in the US 5th Fleet area of operations.

(Navy photo by Petty Officer 2nd Class Michael J. Lieberknec)

Navy Seaman Brice Scraper, top, and Petty Officer 2nd Class Alex Miller verify the serial number of a training missile on the flight deck of the aircraft carrier USS Ronald Reagan in the Philippine Sea, October 5, 2016. The Reagan was supporting security and stability in the Indo-Asia-Pacific region.

(Navy photo by Petty Officer 3rd Class Nathan Burke)

Navy Petty Officer 2nd Class Brianna Caballero maneuvers a harbor patrol boat to load it onto a trailer for maintenance on Naval Support Activity Bahrain, January 6, 2016.

(Navy photo by Petty Officer 1st Class Gary Granger Jr.)

Soldiers offload equipment and supplies from a CH-47F Chinook helicopter after landing on Kahiltna Glacier in Denali National Park and Preserve, Alaska, April 24, 2016. At 17,400 feet, Mount Foraker towers above.Air Force Maj. Steve Briones and 1st Lt. Andrew Kim fly a KC-135 Stratotanker aircraft over Turkey, January 6, 2016. Coalition forces fly daily missions to support Operation Inherent Resolve.Members of the visit, board, search, and seizure team for the guided-missile destroyer USS Gonzalez operate a rigid-hull inflatable boat in the Gulf of Aden, April 26, 2016. The Gonzalez was supporting Operation Inherent Resolve, maritime security operations and theater security cooperation efforts in the US 5th Fleet area of operations.

(Army photo by John Pennell)

Air Force Maj. Steve Briones and 1st Lt. Andrew Kim fly a KC-135 Stratotanker aircraft over Turkey, January 6, 2016. Coalition forces fly daily missions to support Operation Inherent Resolve.Members of the visit, board, search, and seizure team for the guided-missile destroyer USS Gonzalez operate a rigid-hull inflatable boat in the Gulf of Aden, April 26, 2016. The Gonzalez was supporting Operation Inherent Resolve, maritime security operations and theater security cooperation efforts in the US 5th Fleet area of operations.

(Air Force photo by Staff Sgt. Corey Hook)

Members of the visit, board, search, and seizure team for the guided-missile destroyer USS Gonzalez operate a rigid-hull inflatable boat in the Gulf of Aden, April 26, 2016. The Gonzalez was supporting Operation Inherent Resolve, maritime security operations and theater security cooperation efforts in the US 5th Fleet area of operations.Air Force Maj. Steve Briones and 1st Lt. Andrew Kim fly a KC-135 Stratotanker aircraft over Turkey, January 6, 2016. Coalition forces fly daily missions to support Operation Inherent Resolve.Soldiers offload equipment and supplies from a CH-47F Chinook helicopter after landing on Kahiltna Glacier in Denali National Park and Preserve, Alaska, April 24, 2016. At 17,400 feet, Mount Foraker towers above.

(Navy photo by Petty Officer 3rd Class Pasquale Sena)

Sailors move a T-45C Goshawk aircraft on the flight deck of the aircraft carrier USS Dwight D. Eisenhower in the Atlantic Ocean, February 5, 2016. The Eisenhower was preparing for inspections and conducting carrier qualifications.

(Navy photo by Petty Officer 3rd Class Anderson W. Branch)

The guided-missile destroyer USS Carney breaks away from the fleet-replenishment oiler USNS Big Horn after a replenishment at sea in the Mediterranean Sea, August 14, 2016. The Carney was patrolling in the US 6th Fleet area of responsibility to support US national-security interests in Europe.

(Navy photo by Petty Officer 3rd Class Weston Jones)

A Marine Corps MV-22 Osprey aircraft prepares for takeoff from the flight deck of the amphibious assault ship USS Boxer in the Pacific Ocean, August 26, 2016.

(Navy photo by Petty Officer 3rd Class Michael T. Eckelbecker)

Navy Petty Officer 3rd Class Kristen Neufeld performs maintenance on a Mark 38-25 mm machine gun aboard the aircraft carrier USS Carl Vinson at its home port in San Diego, August 18, 2016.

(Navy photo by Seaman Theo Shively)

Navy Petty Officer 3rd Class Brian Evans repairs an antenna system during a replenishment at sea involving the aircraft carrier USS Dwight D. Eisenhower, the guided-missile cruiser USS Monterey, and the Military Sealift Command combat support ship USNS Arctic in the Persian Gulf, September 2, 2016.

(Navy photo by Petty Officer 3rd Class Nathan T. Beard)

Sailors aboard the guided-missile destroyer USS Ross move ropes during a sea-and-anchor detail near Aksav, Turkey, January 7, 2016. The Ross was conducting a routine patrol in the US 6th Fleet area of operations to support US national-security interests in Europe.

(Navy photo by Petty Officer 2nd Class Justin Stumberg)

Navy Petty Officer 3rd Class Trevor Ellam signals to the fleet-replenishment oiler USNS Laramie from aboard the guided-missile destroyer USS Stout during a replenishment at sea in the Persian Gulf, October 14, 2016. Ellam is a boatswain’s mate. The Stout was supporting security efforts in the US 5th Fleet area of operations.

(Navy photo by Petty Officer 3rd Class Bill Dodge)

Marines depart a CH-53E Super Stallion helicopter aboard the amphibious-assault ship USS Makin Island in the Pacific Ocean, October 22, 2016. The Makin Island was supporting the Navy’s maritime strategy in the US 3rd Fleet area of responsibility. The helicopter is assigned to Marine Medium Tiltrotor Squadron 163.

(Navy photo by Seaman Devin M. Langer)

Navy Petty Officer 2nd Class Matthew Fulks motions to crew members on the flight deck of the aircraft carrier USS John C. Stennis in the Philippine Sea, February 24, 2016. The Stennis provides a ready force to support security and stability in the Indo-Asia-Pacific region.

(Navy photo by Seaman Cole C. Pielop)

The guided-missile destroyer USS Lassen patrols the eastern Pacific Ocean, March 10, 2016. The Lassen was supporting Operation Martillo with the US Coast Guard and partner nations within the US 4th Fleet area of responsibility.

(Navy photo by Petty Officer 2nd Class Huey D. Younger Jr.)

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TOMAHAWKS, TOO

The bombing came less than a week after Trump ordered the firing of 59 Tomahawk missiles at a Syrian airfield in response to a deadly nerve gas attack. That raised questions about his plans for North Korea, which has conducted missile and nuclear tests in defiance of U.N. and unilateral sanctions.

"Certainly there's a signaling element as a by-product – possibly being a signal to Syria or North Korea; certainly there is a signal to ISIS that no matter how much you try to hide, no matter how deep you dig, we can still get you," said Mark Cancian, a retired U.S. Marine Corps colonel and ordnance specialist. {nL3N1HM1N5]

Cancian, an adviser at Washington's Center for Strategic and International Studies think-tank, said regular bombs were not able to destroy a tunnel and cave complex.

"You need something with a lot of concussion. It goes off slightly above ground, but it creates a tremendous blast wave that will go deep into a cave and around corners, which frustrate regular munitions."

SEE ALSO: General explains why it's the 'right time' to use huge bomb in Afghanistan

Retired U.S. Air Force General Dave Deptula, a former commander of the air operations center for Operation Enduring Freedom in Afghanistan in 2001, said the GBU-43 was developed to replace the 15,000-pound "Daisy Cutter" bomb he employed there.

The Daisy Cutter, which was first used to clear landing strips for helicopters in Vietnam, was employed partly for the psychological effect of its massive blast.

Deptula, Cancian and U.S. military officials said the United States has an even larger bomb in its inventory - the 30,000 pound (14,000 kg) GBU-57 Massive Ordnance Penetrator (MOP), which would be more effective against North Korea's nuclear test site, given its ability to penetrate reinforced concrete and anti-blast steel doors.

Deptula said the MOAB was designed to create over-pressure to collapse caves and a blast effect over about a mile on soft-to medium ground. The MOB, which has never been employed in combat, was designed to penetrate deep and hardened targets.

SEE ALSO: US may launch strike If North Korea reaches for nuclear trigger

The MOAB and the MOP owe their origins to massive "Tallboy" and "Grand Slam" bombs developed by the British in World War Two for use against Nazi targets such as V-1 and V-2 missile sites and the battleship Tirpitz.

Deptula said that while the decision to drop the MOAB appeared be tactical, he acknowledged the psychological side-effects. (Reporting by David Brunnstrom; Editing by John Walcott, Dan Grebler and Bill Trott)

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