The Cruel Sea:
French Cruiser DeGrasse
by Mike Bennighof, Ph.D.
November 2023

To follow the La Galissonière class light cruisers, France’s Marine Nationale chose a slightly larger design to remain within the bounds of the 1936 London Naval Treaty. France, Britain, and the United States had agreed to limit new cruisers to 8,000 tons’ displacement and a main armament no larger than 155mm (6.1-inch) caliber.

Once again, the Marine Nationale would build a set of three ships; these would have a much greater anti-aircraft capability, making them more suitable as escorts for the new aircraft carriers then at the planning stage and authorized in 1937. The Service Technique des Constructions Navale (STCN, which designed France’s warships) had little room with which to work in the desired improvements. The De Grasse class light cruisers would be only 400 tons larger than La
Galissonière, which would not allow for the quadruple turrets the designers had hoped to employ in the next class of light cruisers.

An early draft had ten 152mm (6-inch) Model 1930 rifles (the same weapon that armed La Galissonière) in one twin turret super-firing over a triple turret forward, and a similar pair at the aft end of the ship. That proved much too heavy, and while an alternative with two triple turrets forward and a quadruple turret aft saved some weight, it still pushed the ship over the limit.

The final version went with three triple turrets, as in La Galissonière, but using a modified version of the dual-purpose mounts deployed in the new Richelieu-class fast battleships. This would allow the guns to be elevated to 70 degrees (compared to 45 degrees in La Galissonière) and also increase their range against surface targets. Richelieu’s Model 1936 turrets could elevate to 90 degrees, but were much heavier than the version proposed for the new cruiser.

Augmenting the ship’s air-defense capability would be three enclosed dual mounts for the new 100mm Model 1933 anti-aircraft gun. This weapon, expected to be very effective, required a large magazine for its high consumption rate, which had to be located directly under the gun mount.

Light cruiser De Grasse under construction.

In practice, the 152mm gun failed in the anti-aircraft role – it lacked a sufficient rate of fire, and could not be trained quickly enough to track fast-moving aircraft. It also consumed a great deal of ammunition. Though designed for an elevation of 90 degrees (and given the wells under the gun breeches to allow firing at such an extreme angle), in guns turned out to only be usable at a maximum elevation of about 75 degrees. The 100mm gun turned out much better, and they would eventually be mounted in Richelieu in place of the 152mm turrets.

To give them the widest possible field of fire, the three 100mm mounts were placed directly behind the aft 152mm turrets, elevated to fire over it. De Grasse would have just one large funnel rather than two; this would both reduce smoke interference with the anti-aircraft suite and provide more room for enlarged seaplane facilities. The new cruiser would have two catapults, one on either beam, with two aircraft (one kept on each catapult); another variation would have included a large hangar amidships, raising the number of seaplanes carried from two to four.

Initially the ship would have carried four torpedo tubes, with a twin mount on either beam amidships to match La Galissonière. This was later increased to a triple mount in each position. She was not fitted to lay mines, but La Galissonière and her sisters received depth charge racks during the war, and this would likely have been true for the De Grasse class as well.

De Grasse would be slightly faster than La Galissonière, designed for 34 knots on 110,000 horsepower. She had twin shafts and a transom stern, like the earlier ship, but a larger power plant divided into two complete sets to assure redundancy in case of battle damage. She had a hull form similar to La Galissonière but slightly finer, and divided into 16 watertight compartments with a double bottom. For her type she had reasonable protection, with a four-inch (100mm) belt and extra care given to her magazines and shell rooms. And like La Galissonière, she had special seals, ventilation, and air circulation systems to guard against poison gas, plus gas masks for all of the crew.

The 1937 Estimates authorized one ship, De Grasse, and the 1938 Estimates two more,
Châteaurenault and Guichen. The Lorient Arsenal laid down De Grasse one week before France declared war on Germany; the other two had not been started at the private shipyards given their contracts and were immediately cancelled. After a brief halt, work resumed on De Grasse and she stood at 28 percent complete when the Germans captured the Arsenal on 22 June 1940.

The Germans considered completing her as an aircraft carrier, a project that made very little sense and very little progress. They left the hull intact, and the Marine Nationale completed De Grasse in 1956 as an anti-aircraft cruiser. She served in that role until 1966, then as a research vessel for French nuclear tests in the Pacific before being scrapped in 1974.

Things go much differently in the world of the Second Great War. The Marine Nationale builds all three cruisers actually authorized, all serving in the Atlantic Fleet, and three which are stationed in French Indo-China. All of them began construction a little earlier than in our own history and are in service when war erupts in August 1940.

You can read all about the French Navy that never was in Fleets of the Second Great War: La Royale.

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

You can order La Royale right here.
Ships late November.

Storyteller’s Bookshelf
            The Second Great War
            Fleets: Imperial Germany
            Fleets: Imperial Russia
            Fleets: La Royale
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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. Leopold feared ocean waves.

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