Grand Slam Was Biggest Bomb Ever Used in Combat

In the world of military technological history, just like in civilian life, bigger hasn’t always been better … but it has darn sure been more memorable.

For example, on the naval history side of the ledger, people remember the WWII Imperial Japanese Navy’s Yamato and Musashi – the world’s largest battleships ever afloat – as well as their sister ship the Shinano – which was converted into the world’s first supercarrier – even though all three of these ships were sunk with heavy loss of life and comparatively little damage inflicted on their U.S. Navy adversaries in return.

Meanwhile, on the aviation side of the ledger, you had the U.S. Air Force’s Cold War-era Convair B-36 Peacemaker heavy bomber, which had the longest wingspan of any combat aircraft but never released its payload in actual combat.

However, when it comes to big *bombs* dropped from aerial platforms, the combat performance record becomes a good bit more auspicious. With that in mind, let’s talk about the heaviest bomb ever made, the Grand Slam.

Grand Slam Gets Started

The Grand Slam bomb – officially designated “Bomb, MC (Medium Capacity) 22,000lb,” which equates to 10 tons – was a British invention. According to the Sheffield Museum’s info page, “ They were produced by Vickers & Co, Sheffield, at their River Don Works during the Second World War … It was designed by Sir Barnes Wallis, a British Aeronautical Engineer, who also created the Bouncing Bomb used in the Dambusters Raid.” 

Additional specifications included a length of 26 feet 6 inches – the tail section comprised 13 feet 6 inches of that total length – a diameter of 3 feet 10 inches, and a blast yield with equivalent to 6.6 tons of TNT. 

The Grand Slam was a successor to the “Tall Boy” bomb, itself quite imposing at 12,000 lbs. (6 tons); these Tall Boys were used to sink the Kriegsmarine battleship Tirpitz in November 1944. It was designed in 1943 and entered production in 1944. It took specially modified Avro Lancaster heavy bombers to carry it; these so-called “B1 Special” Lancasters had the bomb bay doors removed entirely so that a single ‘Grand Slam’ could be carried semi-recessed under the warbirds’ bellies, and the undercarriage was reinforced.

Combat Performance

On 14 March 1945, Nazi Germany first experienced the “shock and awe” of such a bomb. It was a raid flown against the Bielefeld railway viaduct, which was strategically important due to its use as (1) a daily crossing point by over 300 of Nazi Germany’s trains on the Ruhr-Hannover route, and (2) a control point for large numbers of Wehrmacht troops transiting between various front lines.

The lucky RAF pilot in question who got to drop the first Grand Slam “in anger” was Squadron Leader (equivalent of an Major/O-4 in the U.S. Air Force) Charles ‘Jock’ Calder, a proud Scotsman. According to the RAF Memorial Flight Club’s official website:

“At 4.30 pm Calder released the 10-ton ‘Grand Slam’ from 12,000 feet against the two parallel railway viaducts at Bielefeld. This was lower than ideal, but forced by the cloud base. The Lancaster, PD112, leapt up 500 feet as the bomb was released … When the dust and smoke had cleared, more than 400 feet of both viaducts, five arches, had been brought down by the ‘earthquake’ effect. The ‘Grand Slam’ had achieved what more than 3,500 tons of bombs dropped on the viaduct in 54 attacks up to this point had failed to do. The viaduct was closed for the rest of the war, significantly degrading the enemy’s ability to move troops and supplies by rail through the area.”

From there, an additional 40 Grand Slams – out of 99 total built –would be dropped before WWII ended, against additional strategic targets such as U-boat pens, bridges, and coastal batteries. They were used exclusively in the European Theatre of the war, ergo Imperial Japan never got to experience the brunt of the Grand Slam … though needless to say, that particular Axis country would endure even more devastating blasts in the form of the “Fat Man” and “Little Boy,” i.e. the atomic bombs. 

Compared with Newer “Bunker Busters”

Members of Generation X – I’m one of those – and Millennials who haven’t brushed up on their WWII studies are most likely to think of the “Daisy Cutter” – officially the Bomb Live Unit (BLU-82/B) – upon hearing or reading about “bunker buster” bombs, due to their use against Taliban and Al Qaeda cave networks in Afghanistan during the early stages of Operation Enduring Freedom and the Global War On Terror (GWOT). But even that impressive piece of ordnance is no sporting rival, having been first used in 1970 during the Vietnam War. In any event, the Daisy Cutter weighs 15,000 lbs (7.5 tons), a mere 68.1 percent of the Grand Slam’s mass. 

And as I noted months back, South Korea has unveiled the Hyunmoo-4 high-powered missile, which “is estimated to have 2-3 times the destructive power and underground penetration capability of the GBU-28, a laser-guided air bomb of [South Korea’s] Air Force, and the ‘GBU-57’ (also known as the bunker buster).” Mind you, the actual payload of the Hyunmoo-4 is a measly 2 tons; so, in other words, it uses its payload much more efficiently than the Grand Slam did – not to mention greater accuracy and standoff attack capability – but still pales in comparison to the Brits’ “earthquake bomb” for sheer Gigantor-like status. 

Where Are They Now?

The aforementioned Shefield Museums, more specifically the Kelham Island Museum branch, displays the main portion of the Grand Slam, sans lightweight tail. Five other Grand Slams are viewable at the RAF Museum, London, Brooklands Museum, RAF Lossiemouth, Dumfries and Galloway Aviation Museum, and the Battle of Britain Memorial Flight Visitors' Centre at RAF Coningsby. For the benefit of Yanks who lack either the time and/or funds and/or desire to visit the UK, there’s the American-made variant dubbed the T-12 Cloudmaker, at the Air Force Armament Museum at Eglin AFB, Florida. 

About the Author 

Christian D. Orr is a former Air Force Security Forces officer, Federal law enforcement officer, and private military contractor (with assignments worked in Iraq, the United Arab Emirates, Kosovo, Japan, Germany, and the Pentagon). Chris holds a B.A. in International Relations from the University of Southern California (USC) and an M.A. in Intelligence Studies (concentration in Terrorism Studies) from American Military University (AMU). He has also been published in The Daily Torch and The Journal of Intelligence and Cyber Security. 

Image: Creative Commons.