Amatol

Lore & Background

Following the Shell Crisis of 1915 in which the UK did not have enough ordnance due to a lack of explosives, a team at the Royal Arsenal laboratories produced a mixture of ammonium nitrate and TNT, known as Amatol for short. Special factories were constructed for the manufacture of ammonium nitrate by the double decomposition of sodium nitrate and ammonium sulfate in solution followed by evaporative concentration and crystallization. It became the standard filling for British shells and bombs, and while the US also used Amatol, it was never adopted as their principal high explosive—the US primarily used TNT and later Composition B.

Reader's Guide

Amatol exploits synergy between TNT and ammonium nitrate. TNT has higher explosive velocity and brisance, but is deficient in oxygen. The oxygen surplus of ammonium nitrate increases the energy release of TNT during detonation. Amatol allowed supplies of TNT to be expanded considerably, with little reduction in destructive power so long as the TNT content did not fall below 60%. It was widely used during World War II as filler for artillery shells since it blasted lower-grade steel shell bodies into lethal fragments. Modern shells use higher-grade steel, allowing more powerful explosives; filling them with amatol would give poor fragmentation. Amatol is rare today, except in legacy munitions or unexploded ordnance. A derivative, amatex, consists of 51% ammonium nitrate, 40% TNT, and 9% RDX. Ammonite, a civil engineering explosive popular in Eastern Europe and China, is a form of amatol with a 20/80 mixture of TNT and ammonium nitrate.

Did You Know?

• Amatol is hygroscopic, complicating long-term storage; charges were coated with pure molten TNT or bitumen to prevent moisture problems.
• Amatol should not be stored in containers made from copper or its alloys, as it can form sensitive compounds.
• Contrary to popular belief, the warheads of German V-1 flying bombs and V-2 rockets did not contain amatol.

Born of the Shell Crisis

The name Amatol is a portmanteau drawn from ammonium and toluene, the latter being the chemical precursor to TNT. The compound was born out of desperation. In 1915, the United Kingdom faced what became known as the Shell Crisis, a period in which the nation's ordnance production ground to a halt because available explosives could not keep pace with the demands of the Western Front. A team working at the Royal Arsenal laboratories responded by blending ammonium nitrate with TNT, coining the shortened name Amatol for the result. To sustain production, the government erected dedicated factories where ammonium nitrate was manufactured through the double decomposition of sodium nitrate and ammonium sulfate in solution, followed by evaporative concentration and crystallization. The mixture quickly became the standard filling for shells and bombs, and the United States subsequently adopted it as its principal high explosive. In France, a closely related blend of one part dinitronaphthalene to seven parts ammonium nitrate carried the name Schneiderite.

Chemistry and the Oxygen Balance

The effectiveness of Amatol rests on a chemical synergy between its two components. TNT delivers high explosive velocity and brisance but carries a fifty percent oxygen deficiency, which produces the characteristic black smoke of a pure TNT detonation. Ammonium nitrate, by contrast, holds an oxygen surplus that compensates for TNT's shortfall, boosting the total energy released during detonation and shifting the smoke residue to white or grey. The trade-off is that Amatol's explosive velocity and brisance fall below those of pure TNT, but the far lower cost of ammonium nitrate makes the blend economically attractive. As long as the TNT content stays at or above sixty percent, the mixture retains adequate destructive power for most military applications. A practical example: six tons of TNT combined with four tons of ammonium nitrate yields ten tons of high explosive suitable for standard combat use. Because the blend is oxygen-balanced, it performs more effectively than pure TNT in confined or submerged environments such as underground tunnels or underwater. Mixtures dropping to as little as twenty percent TNT were reserved for less demanding tasks.

Iconic Wartime Deployments

Amatol served as the workhorse explosive across both World Wars, filling aircraft bombs, artillery shells, depth charges, and naval mines. Its particular value in World War II lay in its moderate blast characteristics: it shattered the lower-grade steel shell bodies of the era into lethal fragments, whereas more powerful explosives like TNT or RDX would simply pulverize the casing into fine powder, defeating the purpose of fragmentation. Several iconic operations relied on Amatol. The explosive charges hidden aboard HMS Campbeltown during the daring St. Nazaire Raid of 1942 contained the mixture. In September 1943, British X-class midget submarines that planted charges beneath the German battleship Tirpitz carried two saddle charges totaling four tons of Amatol. On the Axis side, warheads for both the V-1 flying bomb and the V-2 rocket also used Amatol as their filling. The compound's versatility made it the default choice for a wide spectrum of military ordnance throughout the conflict.

From Cannery to Legacy

Producing Amatol was straightforward enough that relatively unsophisticated cannery equipment could be adapted for the task. TNT was gently heated with steam or hot water until it melted into a syrup-like consistency, then the correct weight of powdered ammonium nitrate was stirred in. While still molten, the blend was poured into empty bomb casings and left to cool and solidify. Lower-grade mixtures that could not be cast from molten TNT were instead made by thoroughly mixing flaked TNT with powdered ammonium nitrate and compressing or extruding the result. Storage presented challenges: Amatol is hygroscopic, absorbing moisture from the air, so charges were typically coated with a thin layer of pure molten TNT or bitumen. It must never be stored in copper or brass containers, as it can form vibration-sensitive unstable compounds. Today, Amatol has largely been superseded by Composition B, Torpex, and Tritonal in military service, though a civil-engineering variant called Ammonite, typically a twenty-to-eighty TNT-to-ammonium-nitrate blend, remains in use for quarrying and mining in Eastern Europe and China.