M18 Hellcat

American armoured doctrine in the early war years rested on a controversial idea. Tanks, the theory ran, were for exploitation and supporting the infantry; the job of stopping an enemy tank attack belonged to a separate arm — the Tank Destroyer Force — equipped with specialised vehicles that would rush to the threatened sector, ambush the enemy armour and destroy it. The watchwords of this new branch were stamped on its insignia: “Seek, Strike, Destroy.”

The ideal tank destroyer, in this thinking, was not a heavily-armoured slugger but a fast, lightly-protected gun carrier that traded armour for speed and a hard-hitting gun. After the stopgap M10, designers at Buick set out to build the purpose-designed expression of the concept. The result, entering service in 1944, was the 76 mm Gun Motor Carriage M18 — the Hellcat — the only American tank destroyer designed from a clean sheet for the role.

Everything about the Hellcat was built around speed. A lightweight hull, a powerful Continental radial engine, a smooth Torqmatic automatic transmission and torsion-bar suspension gave it a road speed of around 80 km/h — making it, by a wide margin, the fastest tracked armoured fighting vehicle of the entire war, able to outrun almost anything on the battlefield and reposition at will.

Its punch came from the 76 mm Gun M1 in a fully-rotating, open-topped turret — a genuine advantage over the fixed-casemate assault guns like the StuG and Semovente, which had to turn their whole hull to aim. The 76 mm was a sound anti-tank weapon, and with later high-velocity ammunition it could deal with most German armour at sensible ranges, fired from ambush or from the flank where the Hellcat's speed let it strike.

But that speed was bought at a brutal price in protection. The Hellcat's armour was wafer-thin — as little as 12 mm in places — and its turret was open at the top, leaving the crew badly exposed to artillery airbursts, shell splinters and small-arms fire. It could not survive a stand-up fight; its whole way of war depended on seeing the enemy first, hitting hard and being gone before the return fire arrived.

The M18 line was relatively compact. The gun vehicle itself — the 76 mm GMC M18 — was the heart of it, and saw only detail changes across its production run by Buick.

Its excellent, fast chassis was also turned to other uses. The turretless M39 Armored Utility Vehicle stripped off the gun to serve as a fast armoured personnel and supply carrier, prime mover and reconnaissance vehicle — a role in which the Hellcat's speed and reliability made it popular, and in which it soldiered on into the Korean War.

The Hellcat reached the front in 1944 and fought across North-West Europe and Italy. Its defining moment came at the Battle of Arracourt in September 1944, where Hellcat battalions, fighting in fog and using their speed and mobility, ambushed and destroyed large numbers of German Panthers for slight loss — a striking vindication of the tank-destroyer idea when the vehicle was used as intended.

Speed was the whole idea. At nearly 90 km/h the Hellcat was the fastest tracked armoured vehicle of the war, built to race to a threatened sector, strike from ambush with its 76 mm gun and be gone before the enemy could reply. To buy that pace it gave up almost everything else — thin armour and an open-topped turret — a gamble that paid off spectacularly when the vehicle was used as its designers intended.

It proved its worth again in the Battle of the Bulge, racing to threatened sectors and helping blunt the German armoured thrust, including in the defence of Bastogne. Used well — hidden, mobile, striking from ambush and refusing a slugging match — a Hellcat crew could be deadly to far heavier German tanks.

Used badly, it was desperately vulnerable, and its thin, open-topped protection cost lives whenever it was caught in the open or drawn into a stand-up fight. The wider tank-destroyer doctrine itself fell out of favour after the war, as armies concluded that the best answer to a tank was another tank — but as a pure expression of the “fast gun-carrier” idea, the Hellcat was the finest of its kind.

The M18 Hellcat is the purest embodiment of America's tank-destroyer doctrine — a vehicle that staked everything on speed and a good gun, and gave up almost all protection to get them. In the right hands and the right tactics it was lethal, fast enough to dictate the terms of an engagement and quick enough to vanish before the enemy could reply.

Around 2,500 were built, and though the doctrine that produced it did not survive the war, the Hellcat earned a lasting reputation as the fastest, and arguably the most effective, dedicated tank-hunter the US Army fielded. It remains a reminder that on the battlefield, being able to choose the fight — and leave it — could matter as much as armour and firepower.

• Peter Chamberlain & Chris Ellis, British and American Tanks of World War Two (Arms & Armour Press).
• Steven J. Zaloga, M18 Hellcat Tank Destroyer 1943–97 (Osprey, New Vanguard).