Java Sea:
Duguay-Trouin Class Cruisers
by Mike Bennighof, Ph.D.
June 2023

During the years before the First World War, when other nations built large classes of scout cruisers followed by larger and more capable light cruisers, France’s Marine Nationale stood pat. A series of very large armored cruisers, the last of them obsolete before the first steel girder had been laid on the slipway, would fill the role instead.

Just before the Great War broke out, the Marine Nationale began work on a class of modern light cruisers. None had been laid down when war broke out, ending all such projects, and the Service technique des constructions navales (STNC; the naval architect department) spent the war producing more modern alternatives to the pre-war design; like all such offices, the STNC kept churning out blueprints of ships that could not possibly be built under wartime conditions, to keep promising young naval architects employed in vital war work and thus out of the trenches.

The architects re-cast the light cruiser design from a traditional ship mounting eight 138.6mm (5.5-inch) guns in single shielded mounts to very modern one with four powered twin turrets for the same weapons. She displaced 5,200 tons, could make 30 knots, and also carried a dozen torpedo tubes. Project 171, as she was known, matched up very well against the ships of her time but by war’s end would be seriously out-gunned by larger, faster and better-protected British and German light cruisers.

STNC duly prepared a new draft was duly prepared, keeping the torpedoes but swapping the main armament for eight 155mm (6.1-inch) guns, raising the speed to 34 knots and displacement to 8,000 tons. That also nearly doubled the price of the new cruiser, causing the Marine Nationale to cut its planned order of six such ships to just three.

Before the Great War, French ship designs had lagged well behind those of other nations. The new cruiser, to be named Duguay-Trouin, instead set new design standards. She had very fine lines, starting with a clipper bow, to help reach her designed speed. That made for an extraordinarily handsome ship, like most of the interwar French warship designs.

Duguay-Trouin (left) and Primaguet fitting out at Brest Arsenal, 1925.

Duguay-Trouin and two sisters, Lamotte-Picquet and Primaguet, were laid down in 1922 but not in full commission until 1929 thanks to extended machinery deliveries. On trials, she comfortably exceeded the expected 102,000 horsepower from her power plant, pumping out 117,000 horsepower, yet could only make 33 knots compared to a design speed of 34 knots.

The 155mm/50 Mle 1920 could share high-explosive ammunition with the French Army’s 155mm GPF rifle – not a minor consideration in view of the huge stockpiles left over from the Great War – but otherwise was a new design. The complicated re-loading system broke down frequently, and while the contracts had specified a rate of fire of six rounds per minute, in service the guns usually only made half that. They were mounted in true turrets, with 30mm of armor and separate cradles for each of the two guns in each turret.

The heavy torpedo armament, retained from Project 171, followed the pattern of contemporary American and British practice. Twelve tubes in four triple mounts, two on either beam, held the new Mle 1922 550mm torpedo, a big and powerful new weapon with a 310-kilogram warhead. Unusually, Duguay-Trouin also carried a full set of reloads for her tubes. Those were immediately recognized as a potential explosion hazard, and while Duguay-Trouin’s torpedo lockers had hinges to allow the warheads to be jettisoned over the side in case of fire, no later French cruisers carried anything close to this load of seven and a half tons of TNT.

Lamotte-Picquet in drydock. Hong Kong, April 1939.

For anti-aircraft defense, Duguay-Trouin had four 75mm/50 Mle 1922 anti-aircraft guns, a modification of the Mle 1908 gun carried by French pre-dreadnoughts. It proved ineffective in the anti-aircraft role; they would be retained throughout the cruisers’ service life with added splinter shields and modernized fire control. The original six 8mm machine guns, worthless even when new, would be replaced by slightly more useful 13.2mm anti-aircraft machine guns during the 1930’s.

The cruiser had very limited protection: a maximum of 20mm on the belt and over the magazines, and 14mm on the strength deck and over the steering gear. That was sufficient to protect against splinters at best. Turrets, barbettes and the conning tower had 30mm, which would protect against the lightweight guns of Great War-era destroyers but not the heavier weapons they mounted by the conflict’s last years. Duguay-Trouin’s armor certainly would do nothing against ships armed with weapons similar to her own.

That was very common for cruisers designed and built between the wars – their armor was not proof against their own weapons, or often even those of much smaller warships. Duguay-Trouin compensated somewhat with extensive internal subdivision.

Lamotte-Picquet crosses the line, sometime pre-war.

The new light cruisers added a seaplane just after completion, with a catapult on the quarterdeck with fuel stowage beneath the deck. A folding crane mounted alongside the catapult would pluck the seaplane off the water after landing. The seaplane had no protection from the weather and later French cruisers would carry their aircraft amidships.

The design turned out to be adequate at best, though the Marine Nationale would essentially enlarge and repeat it for their first “Treaty Cruisers” armed with 203mm guns, the Duquesne class. While other new cruisers quickly overtook them in terms of combat power, they were economical to operate with reliable machinery – both highly desirable attributes for vessels to patrol distant colonial possessions.

Duguay-Trouin herself began the war with several Atlantic patrol before deploying to the eastern Mediterranean in May 1940. She was interned in Alexandria, Egypt with three other French cruisers. After joining the Free French cause in May 1943, she served in the Mediterranean for the remainder of the war. Afterwards she bombarded coastal targets in Algeria including Muslim villages during the May 1945 massacres of civilians. In 1947 she went to Indo-China to become flagship there, bombarding coastal targets again until her decommissioning in 1952.

Lamotte-Picquet served from 1935 as flagship of the small French squadron in Indo-China, and served as flagship when the French annihilated the Royal Thai Navy at Koh-Chang in January 1941. The cruiser did most of the annihilating herself, and was disarmed in 1942. That didn’t stop U.S. Navy planes from sinking her at her moorings in Saigon in 1945.

Primaguet patrolled the West Indies in the first months of the war, and remained in French West Africa after the Armistice. She was at Casablanca in November 1942 when the Americans attacked, and was destroyed by a combination of battleship shells and aircraft bombs.

Lamotte-Picquet and the Battle of Koh-Change roads appear in our Second World War at Sea: Java Sea.

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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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