On April 13, the US military dropped the most powerful non-nuclear bomb in its arsenal on an ISIS stronghold in Afghanistan.

Nicknamed the "Mother of All Bombs" (but officially called the GBU-43/B Massive Ordnance Air Blast Bomb), the 30-foot-long munition allegedly crushed a network of caves, tunnels, and bunkers dug into a remote mountainside.

The strike was akin to setting off about 11 tons of TNT — a school bus' weight worth of explosives.

However, the attack pales in comparison to an accidental explosion that rocked a coastal town nearly three decades before the first atomic bomb.

On the morning of December 6, 1917, a ship detonated in the harbor of Halifax, Nova Scotia, unleashing a blast equivalent to about 3,000 tons of TNT.

The resulting shockwave instantly killed more than 1,000 people, threw a cargo ship like a bath toy, and created a 50-foot-tall tidal wave.

This is the incredible and horrifying story of the Halifax Explosion: the largest human-made blast in history before the advent of nuclear weapons.

By December 1917, World War I had been raging for three years. Halifax, located on Canada's east coast, served as an important port for shipping troops and supplies to Europe.

_{Nova Scotia Archives & Records Management/Wikimedia} 

On December 6, a Norwegian cargo ship, the SS Imo, was departing Halifax on its way to New York. The ship was en route from the Netherlands to ferry supplies back to a war-ravaged Belgium.

_{Lectures pour tous/Wikimedia Source: NASA Safety Center}

At the same time, the SS Mont Blanc was bound to return to France carrying a host of highly explosive materials: 2,367 tons of picric acid, 62 tons of guncotton, 250 tons of TNT, and 246 tons of benzol in barrels below decks.

_{Public domain. Source: NASA Safety Center}

To exit the Bedford Basin, where the ships were docked, they had to pass through a slim channel. The Imo — behind schedule and on the wrong side of the channel — refused to give way and crashed into the Mont Blanc.

_{Google Maps/Tech Insider}

Although the collision occurred at low speed, the benzol spilled and sparks ignited the entire stockpile of fuel. The Mont Blanc exploded with the force of 2,989 tons of TNT — about 270 times more powerful than a "Mother of All Bombs" blast.

_{Library and Archives Canada/Wikimedia Source: NASA Safety Center}

The shockwave from the blast covered 325 acres of ground and leveled the neighborhood of Richmond. The temperature of the explosion exceeded 9,000 degrees Fahrenheit, vaporizing water around the Mont Blanc — and pushing a 52-foot-tall tidal wave three blocks into town.

_{W. G. McLaughlan/Flickr (CC BY 2.0) Source: NASA Safety Center}

The force of the explosion lifted the Imo out of the water and threw it onto the shore. The Mont Blanc was ripped apart and completely destroyed. Almost no part of the ship survived the explosion.

_{Nova Scotia Archives and Records Management/Wikimedia}

 

Only two parts of the Mont Blanc have ever been located: a 1,140-lb piece of its anchor, found buried more than 2 miles away, and a barrel from one of the ship's guns, which flew 2.35 miles from the blast site.

_{Vonkiegr8/Wikimedia Source: NASA Safety Center}

Much of Halifax was leveled, with 12,000 buildings destroyed or made uninhabitable, leaving a huge portion of the city's population without shelter from the frigid December weather.

^{George Grantham Bain collection/U.S. Library of Congress/Wikimedia}

Almost every window in the city shattered — some reportedly 50 miles away. Even the buildings left standing were severely damaged.

^{Library of Congress}

About 1,600 people died instantly in the blast, and 350 later succumbed to injuries. An estimated 9,000 people were injured in the accident, making 22% of the city's population a casualty.

^{Nova Scotia Archives and Records Management/Wikimedia}

Losses would have been even worse had a railway dispatcher, Vincent Coleman, not halted a train carrying 300 people towards the train station directly in front of the burning ship.

^{L'Illustration/Wikimedia}

Coleman's final action was sending a telegraph warning up the tracks: "Hold up the train. Ammunition ship afire in harbor making for Pier 6 and will explode. Guess this will be my last message. Good-bye boys."

^{The Nova Scotia Museum/Wikimedia Source: Maritime Museum of the Atlantic}

The force of the Halifax explosion was so large that it remained the largest human-made explosion ever until the United States developed atomic weaponry in 1945. Only three later detonations of conventional explosives, all of them deliberate, were larger than the Halifax Explosion.

^{The fireball of the Trinity nuclear bomb test of July 16, 1945.Wikimedia Commons}

Correction: The Halifax Explosion wasn't the largest conventional blast in human history. It's the fourth-largest. The US military's "Misty Picture" and "Minor Scale" tests in the 1980s were the two largest (at 4,000 tons of TNT equivalent), followed by the Heligoland Island/British Bang test in 1947 (at 3,200 tons of TNT equivalent).

Read the original article on Business insider. Follow us on Facebook and Twitter. Copyright 2017.

Read next on Business Insider: Here's the difference between ice cream and other frozen desserts