In a recent Tweet, the Polish Ministry of Defense shared a video taken by one of their Naval ordnance disposal teams. In the video, a massive British bomb from the Second World War exploded underwater, unleashing a massive, unintended explosion. Though accidental, nobody was hurt during the blast. Here’s what we know about the bomb.

Bombs Away

During World War II, both the United States and British developed so-called “earthquake bombs,” intended to take down protected, high-value targets like hardened German U-Boat pens, V-1 and V-2 rocket sites, and other important targets.

One of these designs, dubbed Tallboy, featured a tall, streamlined shape to give the bomb a high terminal velocity and thus increase penetration depth against hardened or underground targets.

Weighing twelve thousand pounds, or nearly fifty-four hundred kilograms, the Tallboy bombs were second only to the larger Grand Slam bomb. They were expensive to build, being largely manufactured individually, rather than mass-produced like their smaller bomb brothers. They were, in essence, hand-made. So great was both their cost to build and worth against particularly tough targets, that bomber crews carrying Tallboys were told not to jettison their ordinance in case they were unable to drop over their target, but to bring the bombs home.

One of the Tallboy’s most noteworthy missions during the war was during a Royal Air Force sortie against the German battleship Tirpitz, one of Germany’s largest ships and thought to be virtually unassailable. Someone recorded video footage of the event.

Bombs Here, Bombs There

According to the Polish Ministry of Defense, the Tallboy that was just decommissioned is the largest unexploded ordnance ever disposed of in Poland. Like a number of European countries that had front lines on their territory during the war, Poland still regularly defuses hundreds if not thousands of bombs each year that lie in wait, unexploded.

Likewise in Germany, an overwhelming amount of ordnance is disposed of yearly, and like this most recent case in Poland, requires evacuating entire neighborhoods to ensure public safety. It’s a dangerous business to defuse old bombs—and this particular case, presented some unusual dangers.

The Tallboy bomb was found by civilian workers while dredging work was being done to deepen a canal. Once found, the plan was to burn out the bomb.

Tallboy bombs were filled with Torpex, an explosive mixture more powerful than TNT that, though now considered obsolete, was favored in torpedoes and depth charges — and Tallboys.

Ideally, the goal was to cut several holes in the bomb’s casing and light the explosive mixture. Rather than exploding, explosive ordnance technicians hoped to in effect burn out the bomb. Plans didn’t go exactly according to plan this time though, according to the Polish Ministry of Defense.

The lieutenant commander of the 8th Coastal Defense Flotilla, G. Lewandowski explained in a Tweet that “the deflagration process turned into detonation. The object can be considered neutralized, it will not pose any more threat to the Szczecin-Swinoujscie shipping channel.”

Postscript

Though there are no doubt hundreds of thousands of unexploded munitions still littering Europe today, this may have been the last Tallboy explosion ever. Be sure to take a look.

Caleb Larson is a Defense Writer with The National Interest. He holds a Master of Public Policy and covers U.S. and Russian security, European defense issues, and German politics and culture.

This article first appeared last year and is being republished due to reader interest.