Roma vs Bismarck
Two fast battleships laid down within a year of each other, built for two different seas. On the specification the Italian ship wins the gun column. In practice her guns were the problem.
They belong to the same moment. Roma and Bismarck were both fast battleships of about 30 knots, both completed early in the war, both sunk before either had a long career — and both were their navies' answer to the same question, asked in different seas. The Italian ship was built for a closed sea in which the enemy was always within a day's steaming; the German for a raiding cruise into an ocean.
The interesting comparison is not which was bigger. It is that they solved the two central problems of a battleship — how to hit, and how to survive being hit — in ways that reverse when you move from the specification to the record. The gun that is superior on paper belonged to the ship that could not group its salvos; the armour scheme that was the more modern in conception belonged to the ship that never once fired her main battery at an enemy warship.
| RN Roma | KMS Bismarck | |
|---|---|---|
| Commissioned | 14 June 1942 | 24 August 1940 |
| Main battery | 9× 381 mm /50 (3×3) | 8× 380 mm /47 (4×2) |
| Shell | 884.8 kg APC at 850 m/s | 800 kg APC at 820 m/s |
| Penetration, side | 510 mm at 18,000 m | 419 mm at 18,000 yd (16,459 m) |
| Penetration, deck | 73 mm at 18,000 m | 75 mm at 18,000 yd (16,459 m) |
| Rate of fire | 1.3 rounds a minute | 2.3–3 rounds a minute |
| Ammunition | 74 rounds per gun · 666 in all | ~125 per gun · about 1,004 in all |
| Barrel life | 110–130 rounds | 180–210 rounds |
| Belt armour | 70 mm decapping plate + 280 mm cemented, inclined 11–15° | 320 mm over 70% of the waterline · 145 mm upper belt |
| Deck armour | 150 mm over the magazines, 162 with plating | 100 mm over the magazines |
| Turret faces | 380 mm | up to 360 mm |
| Underwater protection | Pugliese drum, 3,800 mm, for a 350 kg charge | 45 mm bulkhead, 3–5.4 m inboard |
| Full-load displacement | ~45,500 t | ~50,300 t |
| Range | ~3,920 nmi at 20 kn | ~8,500 nmi at 19 kn |
| Crew | ~1,830 | ~2,200 |
| Fired on an enemy warship | Never | Hood, Prince of Wales, Rodney, King George V |
The two penetration rows are not quite measuring the same thing, and the difference favours the German ship. Italian figures are published against ranges in metres, German ones against ranges in yards, so Bismarck's 419 mm was calculated at 16,459 m — about a mile and a half closer than the range at which Roma is credited with 510 mm. Both sets come from the same US Navy empirical formula, and both are calculations rather than firing trials.
The 381 mm /50 Ansaldo-OTO was the most powerful 15-inch gun any navy took to sea. It threw an 884.8 kg shell at 850 m/s against the German gun's 800 kg at 820, and by the same calculation method it defeated 510 mm of vertical armour at 18,000 m where the 38 cm SK C/34 managed 419 mm at a range half a mile shorter. Roma also carried nine guns to Bismarck's eight, and the heavier of the two turret faces. Every static measure of firepower belongs to the Italian ship.
Then the salvos land, and the order reverses. The Italian gun's known defect was dispersion: shells left the muzzle over-spun by a uniform 1 in 30 rifling driving them at 850 m/s, over-stabilised so that the projectile's axis stopped following the curve of its own trajectory, and the scatter widened with range. The German gun had no such problem and fired more than twice as fast — 2.3 to 3 rounds a minute against 1.3 — from magazines holding 1,004 rounds against 666. Over ten minutes of action Bismarck could put roughly twice as many shells in the air, and they went where they were aimed. The record is the proof: Bismarck destroyed HMS Hood with her fifth salvo at some 15,000 m.
The schemes are opposite in conception. Roma's belt is a modern idea: a 70 mm decapping plate standing off from 280 mm of cemented armour, inclined 11–15°, the outer plate meant to strip the cap off an incoming shell before it reached the plate that mattered. Bismarck's is the older Jutland arrangement: 320 mm covering some 70 per cent of the waterline, backed by the turtleback slopes, with a low armoured deck. Roma carried far more armour where it counted against long-range and air-delivered weapons — 162 mm over her magazines against 100 mm — while Bismarck covered more of her length and kept the sea out of her citadel through several hours of point-blank battleship fire. Each scheme did well what it had been designed to do.
The endurance figures give the two ships away. Roma could steam some 3,920 nautical miles at 20 knots; Bismarck 8,500 at 19 — more than twice as far, because she was meant to disappear into the Atlantic and stay there. Roma never needed the range and never had the fuel: the Regia Marina's oil shortage kept her at anchor for much of a career that lasted fifteen months. It is the reason for the last row of the table. Bismarck fought Hood and Prince of Wales in the Denmark Strait and then Rodney and King George V off Brittany; Roma never fired her 381 mm guns at an enemy warship, and was sunk on her way to surrender by a Fritz X guided bomb.
As a gun platform, Roma was the better ship and the worse weapon. She carried more guns, a heavier shell, a faster shell, more penetration and a thicker deck, and she could not reliably put a salvo into a target because the shells were spun too hard to fly straight. Bismarck carried the second-best 15-inch gun of the war and hit with it — five salvos to destroy the most famous warship in the world.
What separates them in the end is not engineering but employment. Bismarck was sent to do the thing she had been built for, and did enough of it in nine days to require the concentration of most of the Home Fleet to stop her. Roma spent her fifteen months mostly at anchor for want of fuel, and her one distinction is a grim one: she is the first capital ship in history destroyed by a guided weapon. Neither ship was defeated by the other kind of battleship. Both were beaten by aircraft — one by a torpedo that jammed a rudder, the other by a bomb steered onto her deck from three miles up.
- Erminio Bagnasco & Augusto de Toro, The Littorio Class: Italy’s Last and Largest Battleships (Seaforth).
- William H. Garzke, Robert O. Dulin & William Jurens, Battleship Bismarck: A Design and Operational History (Naval Institute Press, 2019).
- Marco Santarini, “Gunfire Dispersion of Large Italian Naval Guns: The Strange Case of the 381/50 Ansaldo-OTO mod. 1934 Gun”, Warship International 57/4 (December 2020).
- Roger Chesneau (ed.), Conway’s All the World’s Fighting Ships 1922–1946 (Conway Maritime Press).