The U.S. military dropped the most powerful non-nuclear bomb in its arsenal Thursday on a cave and tunnel complex that it said was used by Islamic State fighters in eastern Afghanistan, a stark reminder of a U.S. war now in its 16th grinding year.The behemoth bomb, officially called the Massive Ordnance Air Blast, or MOAB, is also known as the "mother of all bombs." It is 30 feet long, weighs nearly 11 tons and produces a devastating above-ground explosion that sends a mushroom cloud roiling high in the sky.Originally developed for the 2003 invasion of Iraq, the MOAB has never been used in combat before.Like the U.S. retaliatory missile strike in Syria last Friday, however, use of the monster munition in Afghanistan is more symbolic than tactical since it is unlikely to change the course of America&rsquo;s longest war.President Trump praised the attack as a "very, very successful mission." He indicated that he had given the Pentagon a free hand to use the weapon as part of his vow to step up the war on Islamic State."We have given them total authorization and that&rsquo;s what they&rsquo;re doing and frankly that&rsquo;s why they&rsquo;ve been so successful lately,&rdquo; he told reporters at the White House. &ldquo;If you look at what&rsquo;s happened over the last eight weeks and compare that really to what&rsquo;s happened over the past eight years, you&rsquo;ll see there&rsquo;s a tremendous difference, tremendous difference.&rdquo;ALSO:&nbsp;U.S. military says misdirected airstrike in northern Syria killed 18 allied fightersWhile the Pentagon&rsquo;s formal rules of engagement have not changed, military commanders appear to have taken greater liberties in recent weeks &mdash; and made more mistakes.A series of misdirected U.S. attacks in Iraq, Syria and Yemen have led to a noticeable increase in reported civilian casualties. Earlier Thursday, the U.S. military announced an air strike this week had accidentally killed 18 rebel fighters battling Islamic State in northern Syria in the worst friendly-fire incident of that conflict.The military said the giant MOAB was dropped from the rear door of an MC-130 cargo plane at 7:32 p.m. Thursday as part of a U.S.-backed offensive on an Islamic State stronghold in Achin district in Nangarhar province.The bomb initially falls with a parachute to slow its descent and give the aircraft time to get away safely. Then a GPS system guides the bomb to its target.The munition detonates before it hits the ground, igniting a flammable fuel mist that supposedly obliterates everything in a 1,000 yard radius, sends a lethal shock wave more than a mile and a half away, and creates a mushroom cloud nearly five miles high.&ldquo;The strike was designed to minimize the risk to Afghan and U.S. forces conducting clearing operations in the area while maximizing the destruction" to the militants, the statement said.Gen.&nbsp;John W. Nicholson, commander of U.S. forces in Afghanistan, said the militants used bunkers and tunnels to &ldquo;thicken their defense.&rdquo;&ldquo;This is the right munition to reduce these obstacles and maintain the momentum of our offensive," Nicholson said.White House spokesman Sean Spicer said the massive bomb targeted tunnels and caves that militants &ldquo;used to move around freely, making it easier for them to target U.S. military advisers and Afghan forces in the area.&rdquo;He said U.S. commanders &ldquo;took all precautions necessary to prevent civilian casualties and collateral damage as a result of the operation." Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 Speaking by phone from Achin district, Sher Nabi, a commander with the Afghan Local Police, said the bomb landed about a half mile outside the town of Shogal, near the border with Pakistan.Nabi, who commands a 60-man unit of the government militia, said Afghan security forces have carried out operations in the area for several days against suspected Islamic State supporters.Nabi said that the bomb killed "many militants" and destroyed their weapons. There were no immediate reports of civilian casualties.The air strike apparently was in the same area where Army Staff Sgt. Mark R. De Alencar, a 37-year-old Green Beret from Maryland, was killed on Saturday after coming under fire.He was the first American service member killed in combat this year in Afghanistan, and the 1,833rd since the U.S.-led invasion in late 2001.The GBU-43 bomb was developed in 2002 to &ldquo;put pressure on then-Iraqi dictator Saddam Hussein to cease and desist or the United States would not only have the means but use them against the unpopular tyrant,&rdquo; the Air Force said in 2005 news release.ALSO:&nbsp;White House calls Russian denials on Syrian gas attack a 'coverup'It was tested at Eglin Air Force Base in Florida but was not used in Iraq. On March 11, 2003, a test produced a mushroom cloud visible from 20 miles away, the release said.Another U.S. munition, officially called the Massive Ordinance Penetrator, or MOP, is designed to penetrate hardened bunkers. At 30,000 pounds, it is even heavier than the MOAB but carries less explosive power.Special correspondent Sultan Faizy contributed from Kabul, Afghanistan.