The Cruel Sea:
French Heavy Cruisers, Part One
by Mike Bennighof, Ph.D.
August 2022

Keeping within treaty limits, France only built one cruiser of the Algérie class, but would be able to commission new ones starting in 1942, when the oldest cruisers built under the agreements, the Duguay-Trouin-class light cruisers, began to reach 20 years of age. Design work on a new cruiser began in 1939, still keeping within the size and gunnery limits agreed at Washington in 1922: 10,000 tons’ displacement and 203mm (eight-inch) guns.

This would be the fifth heavy cruiser built for the Marine Nationale since 1926, and so the design had the initial designation of C5. Cruiser C5 would also meet the treaty limits of 10,000 tons and 203mm guns, but would otherwise be a significant break with previous French practice. She would have similar hull form, bridge structure and armor scheme to the previous French heavy cruiser, Algérie, an outstanding design well worth emulating.

Cruiser C5 would be very slightly shorter than Algérie, with the real difference coming in her armament layout: three triple turrets, compared to four twin turrets for all previous French heavy cruisers. They probably would have carried the same Model 1924 50-caliber 203mm rifles as all preceding French heavy cruisers (including Algérie; Algérie had a new-model turret with heavier armor which seems to have confused some authors).

The armament’s layout followed the design of the De Grasse-class light cruisers, the lead ship of which had just been laid down. Three triple turrets gave the new cruiser one more heavy gun, and allowed for slightly more armor – and extra space for additional anti-aircraft weapons and for aircraft handling facilities. She would also carry six torpedo tubes in two trainable triple mounts, one on either beam (beneath the aircraft handling area).

Like De Grasse, Cruiser C5 would carry the dual-mount 100mm 45-caliber Model 1933 anti-aircraft gun, also usable against surface targets. This same weapon had equipped Algérie and the modern French fast battleships starting with the Richelieu class. It was semi-automatic, able to fire 16 rounds per minute in tests and about 10 rounds per minute under service conditions, which made it somewhat slower than contemporary heavy anti-aircraft guns.

The 37mm ACAD mount installed on the sloop Amiens for testing; the gunnery director is to the left covered by canvas.

For close defense, the cruiser had the new 37mm ACAD twin-mount automatic anti-aircraft guns. This was a sophisticated system featuring high muzzle velocity (so that the projectile reached its target with minimal flight time, improving accuracy) and a heavy bursting charge (so that a single shell could hopefully bring down the target aircraft). Those conflicting requirements led to adoption of a complicated loading system with six-round cartridge boxes brought up from the ready-use rack located a deck below the gun mount itself.

That high velocity and heavy shell added up to severe vibrations, and so the director and rangefinder were located in a separate tower directly behind the gun mount. The gun captain controlled the weapon from there by remote control (one director tower sometimes controlled two separate gun mounts). The problematic velocity/shell weight combination, plus the high rate of fire (over 100 rounds per minute in sustained firing) also resulted in rapid barrel wear, within minutes at maximum rate of fire (172 rounds per minutes). Only one mount was completed before the fall of France; it was deployed at Dunkirk on a small French warship and appears to have performed well.

Cruiser C5 would also have far more powerful turbines than Algérie, generating 100,000 horsepower compared to 82,000 for the previous heavy cruiser, and raising her top speed from the 31 knots of Algérie to 32.5 knots.

The architects laid out two versions of Cruiser C5: one with aircraft, and one without. The aircraft-carrying cruiser would have two catapults, located amidships with one on either beam. Each catapult had its own crane to pluck aircraft off the water. The cruiser had no hangar: the aircraft would usually remain on the catapult when not in use but could be rolled on and off it to a pad just aft of the catapults where the plane could be serviced.

Cruiser C5-A3 (the aircraft-carrying variant chosen for evaluation, over A1 and A2) would carry just two planes, one Loire 130 flying boat for reconnaissance (the standard French shipboard plane) and one Loire 210 seaplane fighter for air defense of the ship. The Loire 210 proved an abject failure; only 20 were made, five of which suffered structural breakdowns within weeks of entering service, and the surviving aircraft were withdrawn from use and scrapped.

The unsuccessful Loire 210 seaplane fighter.

The other variant (SA, or sans aviation) used the space devoted to the aircraft for additional anti-aircraft weapons. Where A3 had five 100mm twin mounts, SA had seven, and instead of four 37mm mounts, SA had six. That required additional magazines belowdecks (anti-aircraft batteries being prodigious consumers of ammunition) and the number of personnel required to man the batteries and the additional directors exceeded the number of crewmen who had manned the aircraft detachment. In short, SA was a much more cramped ship, and the designers may have been aiming at this conclusion, to assure that A3 would be chosen.

The outbreak of war assured that neither A3 nor SA would be selected; once hostilities began, the peacetime limits on ship size no longer applied. The design was re-cast starting in early 1940, keeping the same dimensions but raising the displacement to 14,500 tons. The additional weight went to more protection, and more powerful machinery to move the heavier ship at the slightly higher speed of 33 knots (compared to 32.5 knots for either A3 or SA).

This ship, named Saint-Louis, would have been a big, well-protected ship equivalent to the American Baltimore class. Her exact details are unclear, such as the number of catapults for her aircraft. She would have had the same main armament as the earlier designs, with six 100mm twin mounts, splitting the difference between the earlier designs, and six 37mm ACAD mounts, like SA. Torpedo armament would have remained the same.

Three of the new heavy cruisers figured in the new construction program proposed in January 1940 and approved on 27 May 1940 – one day after the British Expeditionary Force began evacuating from the beaches of Dunkerque. Even in January this was a mere paper exercise – all new construction had halted in French shipyards. There was no prospect of warship construction resuming in the near future, let alone the laying down of new major vessels.

That didn’t stop us from providing Saint-Louis and three sister ships in Second Great War at Sea: The Cruel Sea, our alternative-history expansion set. We went with the one-catapult version, which still provides for a well-protected and fast cruiser, well-suited to the North Atlantic environment.

You can order The Cruel Sea right here, right now.

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Mike Bennighof is president of Avalanche Press and holds a doctorate in history from Emory University. A Fulbright Scholar and NASA Journalist in Space finalist, he has published a great many books, games and articles on historical subjects; people are saying that some of them are actually good. He lives in Birmingham, Alabama with his wife and three children. He will never forget his Iron Dog, Leopold.

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