The Tank: From a Water Closet Code Name to the Iron Triangle and APS

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In 1915 a secret British committee that included Winston Churchill was developing land cruisers to break the trench stalemate of World War I. Shipments were first to be labeled water carriers, until the committee secretary realized the abbreviation WC meant water closet, so they settled on tank. The idea of mobile protected firepower was ancient: Han general Wei Qing ringed armored wagons against the Xiongnu around 119 BC, Jan Žižka armed war wagons in the Hussite Wars, and Leonardo da Vinci sketched a hand-cranked fighting vehicle. It only became practical when the internal combustion engine, steel plate and the agricultural caterpillar track came together. Engineers at the White Hart Hotel in Lincoln built Little Willie, which led to the Mark I, first used at the Somme in September 1916.

The Mark I was slow, roasting and full of fumes, and commanders sent tanks out in small groups. The 1918 French Renault FT set the lasting layout of rear engine and rotating turret. In 1940 German panzer divisions with a two-way radio in every tank beat French forces whose better-armored Char B1s often had none. Mass production then won out over the complex Tiger, with about 65,000 T-34s and over 40,000 Shermans built, and over 10,000 tanks at Kursk in 1943. Cold War main battle tanks faced the iron triangle of firepower, protection and mobility, answered with Chobham composite armor, the M1 Abrams gas turbine, and now active protection systems against cheap missiles.

• Robert Falcon Scott tested motorized tracked vehicles on Antarctic ice in 1911, years before tracks crossed barbed wire in France.
• Male tanks carried naval cannon in side sponsons, while female tanks carried machine guns to protect them from infantry.
• Ceramic layers in Chobham armor shatter and disrupt the superheated copper jet of a shaped-charge round.
• The Abrams' 1,500 horsepower turbine pushes over 60 tons to 45 miles per hour but demands a constant train of fuel trucks.
• Israel's Trophy system uses millimeter-wave radar to detect incoming missiles and fires explosively formed shrapnel to destroy them in the air.