“These Torpex heads carry an awful wallop.”

SOME CALLED IT cyclonite, hexogen or even cyclotrimethylenetrinitramine. It was a key ingredient in Composition B, PE-4 and C-4. The British simply named it RDX. Yet regardless of the appellation, it was the most lethal conventional high-explosive of the Second World War.

RDX or ‘Research Department Explosive,’ also dubbed Torpex, was surprisingly stable yet twice as powerful as TNT. Eventually, it would be used to blast through the hulls of Hitler’s U-boats, blow gaping holes in enemy dams in the Ruhr Valley and knock out bridges, railroad tracks and power stations across Nazi-occupied Europe.

Pioneered by chemists in Germany in the late 19^th Century, by the 1930s, military engineers in both Great Britain and the Third Reich were exploring ways to use this miracle substance as a new wonder weapon. During the early years of the Second World War, both the Allies and Axis began producing RDX, which could come in granular pellet form or as a moldable plastic putty, in limited quantities. But by 1944, the United States alone was producing 50 million pounds of the stuff a month.

Dr. Colin F. Baxter, author of the upcoming book The Secret History of RDX reveals the remarkable story behind this war-winning invention and how it ultimately helped deliver the Allied victory. Here, Baxter shares with MilitaryHistoryNow.com seven facts about RDX.

By Dr. Colin F. Baxter

It Made Waves in the Battle of the Atlantic

RDX/Torpex was integral to the Allies’ aerial depth charge, which at long last provided RAF Coastal Command antisubmarine aircraft with the “knockout” punch needed against Hitler’s heavy hulled U-boats. Since the war’s earliest days, German submarines threatened the Atlantic lifeline between North America and the United Kingdom. Difficult to sink with ordinary TNT depth charges, new RDX versions of the weapons proved decisive in ending the reign of the “wolf packs.” And without victory in the Battle of the Atlantic, there could be no Allied invasion of Nazi-occupied Europe, at least from the West. In the climactic year of 1943, Torpex-loaded aerial depth charges sank 87 U-boats, out of 219 destroyed in 1943, helping to shift control of the seas away from Germany and to the U.S. and Great Britain.

It Powered the Strategic Air Offensive

From 4,000-pound blockbusters and dam-busting “Upkeep” bouncing bombs, to 12,000 pound “Tallboys” and 22,000-pound “Grand Slam” earthquake bombs, all were filled with RDX/Torpex. In fact, the super-explosive was precursor of today’s bunker-busting, MOAB bombs. In November 1944, Tallboys dropped from Lancaster bombers delivered the final blow to the German battleship Tirpitz, which had harried British naval forces for five years but had averted destruction in numerous attacks. The mighty warship ended up “like a stranded whale” following a trio of direct hits from the massive British bombs.

It Was the Silent Service’s Not-So-Silent Weapon

American submarine commanders in the Pacific and Far East demanded more powerful torpedo warheads than those loaded with TNT. So, Admiral William H. P. Blandy, the chief of the Bureau of Ordnance, pushed for the production of RDX in the United States. After the USS Wahoo reported sinking the Japanese freighter Kanka Maru in 1943 with one such weapon, the sub’s skipper enthusiastically reported: “These Torpex heads carry an awful wallop.”

It Was the Weapon-of-Choice for Allied Saboteurs

British SOE agents and American OSS operatives, in cooperation with resistance cells in Nazi occupied Europe, used RDX in the form of C-4 plastic explosives to destroy railroad track, bridges and other targets. In November 1942, SOE agents and Greek saboteurs used the new explosive to destroy the Gorgopotamus gorge viaduct, and the railway track that crossed it.

It Gave  the “Hedgehog” a Lethal Kick

The 24-barrel antisubmarine weapon known as the “Hedgehog” fired a pattern of Torpex-filled projectiles about 200 yards ahead of a destroyer-escort. Unlike depth charges which were triggered by changes in water pressure, the “Hedgehog” was a precision weapon that only exploded on contact with the U-boat’s hull. The USS England would famously sink six Japanese ships over a period of 12 days using Torpex-firing Hedgehogs. They were equally devastating in the North Atlantic.

An Army of American Workers Mass-Produced the Stuff

The Great Holston Ordnance Works of Kingsport, Tennessee, which is where RDX was mass produced, is one of the great unknown American production stories of World War Two. In 1941, there was no likelihood of large-scale American manufacturing of RDX. Such an idea seemed like fantasy. The subsequent mass production of RDX has been described as one of the “great chapters of the war epic.” On what had once been rolling pastureland, the U.S. government authorized the construction of Holston Ordnances Works which would produce RDX. Nearly 18,000 workers were employed in the construction of the massive and secret RDX plant, built at a cost $100 million.

It Triggered the “Fat Man”

RDX was also a critical part of the “gadget” that triggered the the atom bomb dropped on Nagasaki that finally ended World War Two. The weapon depended on a number of shaped charges (“lenses”) composed of Composition B obtained from Holston Ordnance Works. These were placed around the bomb’s spherical plutonium core. When all the smaller charges were triggered simultaneously, the implosion process compressed the plutonium resulting in an instantaneous detonation that delivered a blast equal to 21,000 tons of TNT.

Colin F. Baxter is the author of The Secret History of RDX. He is a professor emeritus of history at East Tennessee State University and former chair of the Department of History. He is the author of The Normandy Campaign, 1944: A Selected Bibliography; The War in North Africa, 1940–1943: A Selected Bibliography; Field Marshal Bernard Law Montgomery, 1887–1976: A Selected Bibliography; and coeditor of The American Military Tradition from Colonial Times to the Present