SU-100

By the summer of 1944 the Red Army’s standard tank destroyer, the SU-85, was losing its edge. Its 85 mm gun had been a fine answer to the Panther and Tiger in 1943, but as German frontal armour thickened it could no longer be relied on to punch through at battlefield ranges. The Soviets needed a heavier weapon on the same cheap, reliable running gear — and they needed it quickly.

The T-34’s turret ring was too small to swallow a much larger gun, so the designers at the Uralmash plant took the well-worn Soviet path: strip off the turret and build a fixed casemate around a big gun instead. Led by L. I. Gorlitskiy and approved in July 1944, the new vehicle kept the T-34-85’s hull, its 500 hp V-2 diesel and its running gear almost unchanged, and mounted the one thing that mattered: a 100 mm gun heavy enough to kill anything the Germans could field.

The heart of the SU-100 was the 100 mm D-10S, a weapon adapted from the B-34 naval anti-aircraft gun. Some 56 calibres long, it fired a 15.9 kg armour-piercing shell at about 900 m/s and could bore through roughly 150 mm of armour at 1,000 m — enough to defeat a Panther head-on and a Tiger at ordinary combat range. A single well-placed round would disable almost any German vehicle it met.

That gun would prove the most important thing about the whole design. Reworked as the D-10T, it went on to arm the T-54/55 — the most-produced tank in history, built in the order of 100,000 examples — so the ballistic heart of this 1944 tank destroyer stayed in front-line service, somewhere in the world, into the twenty-first century. Few wartime weapons had so long an afterlife.

Everything else was built to get that gun into action cheaply. Protection was concentrated where it counted: a well-angled 75 mm upper glacis — the T-34’s famous sloped front carried over — with a heavy mantlet and a distinctive commander’s cupola bulging from the right of the fighting compartment for all-round vision. On the proven ~31.6-tonne chassis it kept good mobility, roughly 50 km/h on roads, so it could keep pace with the tank brigades it supported.

The compromises were those of any turretless design. The gun traversed only about 16° before the whole hull had to be swung to aim; the long barrel left the vehicle nose-heavy; and the four-man crew worked a slow, cramped drill in a compartment that filled with fumes from the big gun — early vehicles gained an extra ventilator to clear the smoke. It was a specialist ambush weapon, not a tank, and it was used like one.

Production began at Uralmash in September 1944, and the first SU-100s reached the front that winter. They were not parcelled out to the infantry but concentrated in self-propelled artillery brigades of the High Command reserve — around 65 vehicles each — to be massed at the decisive point against a German armoured thrust.

Their first serious fighting came in Hungary in January 1945, in the grinding battles around Budapest, where the ability to kill Panthers from standoff distances set them at once apart from the 85 mm vehicles they supplemented. But the battle that would define the SU-100 was still a few weeks away, on the marshy ground west of a Hungarian lake.

On 6 March 1945 the Germans launched their last major offensive of the war — Operation Frühlingserwachen (“Spring Awakening”) — around Lake Balaton, throwing Sepp Dietrich’s 6th SS Panzer Army, King Tigers included, against the 3rd Ukrainian Front in a bid to hold the last oil fields still feeding the Reich.

The Soviets had prepared a defence in depth, and the 207th, 208th and 209th Self-Propelled Artillery Brigades committed over 180 SU-100s to it. Firing from concealed positions layered back across the muddy terrain, they let the panzers come on and then broke them at killing range. In little more than ten days the offensive was bled white — German armoured losses ran into the hundreds of vehicles, many bogged in the spring thaw and finished off from ambush — and the drive to the Danube collapsed. Within weeks the Red Army was at the gates of Vienna.

Around 1,150 SU-100s had been finished by the end of the war in Europe, but the line did not stop there: production continued in the USSR after 1945 and, through the 1950s, under licence in Czechoslovakia as the SD-100. The type then soldiered on with Soviet-aligned armies for decades.

It kept turning up wherever Soviet equipment went to war. Egyptian SU-100s fought at Suez in 1956, again in the Six-Day War of 1967 and the Yom Kippur War of 1973; others saw action in Angola. A design frozen in 1944 was still being fired in anger more than thirty years later — a measure of how right the Soviets had got the basic recipe of gun, engine and hull.

The SU-100 was the summit of the Soviet wartime tank-destroyer line: fast, mechanically simple, and hitting far harder than anything before it. It handed Red Army commanders a cheap, mass-producible vehicle that could kill the heaviest German tanks at everyday ranges, and it was used with real doctrinal skill — held back, massed, and sprung from ambush.

It arrived too late for many of the war’s battles. But at Balaton it did precisely what it had been built to do: stop a massed panzer offensive dead, and help turn the last German attack of the war into its final rout.

• Steven J. Zaloga, Soviet Tanks and Combat Vehicles of World War Two (Arms & Armour Press).
• Steven J. Zaloga, Armored Champion: The Top Tanks of World War II (Stackpole Books).
• Mikhail Baryatinskiy, Soviet Self-Propelled Guns 1941–1945.
• Robert Forczyk, Tank Warfare on the Eastern Front 1943–1945 (Pen & Sword).