203 mm/50 Modèle 1924: The gun of the French heavy cruisers

French 203 mm/50 model 1924 was used by the French heavy cruisers during the Second World War, most notably Colbert and Dupleix. It came equipped with SAP and HE shells, with the latter having a very large explosive filler compared to the SAP shell but poor penetration, while the former having just slightly larger explosive filler than SAP but offering a contact fuse, which might be preferable under some circumstances. Lacking a dedicated AP shell, it struggles to deal with heavily armoured cruisers.

Shell types

Comparison with foreign counterparts

Compared to its peers, the gun has an average muzzle velocity, average rate of fire, and above average horizontal targetting speed. Its biggest weakness is the lack of the dedicated AP shells, which makes the gun unsuitable to deal with any heavily armoured target, even some of the heavy cruisers, like the Admiral Hipper-class. Explosive filler of the HE shells is also below average. Where the gun shines, however, are its SAP shells. Having by far the largest explosive filler among its peers, it’s able to deal an outstanding amount of damage. This is done by having a lower penetration than most of the other comparable shells, but it’s still able to penetrate the majority of light cruisers

HE

SAP / AP

Usage in battles

The gun is used similarly to other 203 mm cruiser guns, but lacks AP or HE-TF shells, making it difficult to challenge heavily armoured targets or airplanes.

• Battleships are immune to your SAP shells. Instead, use HE and try to ignite and incapacitate the crew of exposed stations (e.g. anti-air guns). There are very rare exceptions, such as the aft magazine on Kurama, which can be damaged by shrapnel — a few hits may eventually detonate the magazine. But it is an extremely unreliable method that relies on an excellent knowledge of armour schemes (and/or luck).
  
• Battlecruisers are very rarely targets for the 203 mm, as they tend to be at even higher BRs than battleships. The overall handling of them is the same as for battleships. And, much like battleships, care should be taken to avoid drawing their attention.
• Heavy Cruisers have highly varied armour schemes, ranging from being as easy to destroy as light cruisers (e.g. Futuraka) to being impossible to ammo rack with the 203 (e.g. Pola). Overall, they are challenging targets, and extra care should be taken when choosing the range and angle of engagement, as your poor penetration will frequently be an issue.
• Light Cruisers, except for those that are heavily armoured in higher BRs (e.g. La Galissonnière) are generally the perfect targets for your SAP shells. Adding one or two HE broadsides to the mix may improve the casualty rate on the enemy vessel if you are not aiming to destroy it through ammo racking.
• Destroyers are the easiest targets and are generally best dealt with using SAP shells. Try to aim below the guns of the ship to detonate their ammo racks.
• Coastal vessels are typically best dealt with using HE shells, as you do not have to worry about overpenetration, and the large explosive filler will still inflict substantial damage. There are two exceptions to this rule where using SAP shells is beneficial: heavily armoured coastal vessels (e.g. MBK 161) or approaching/departing frigates (like the SKR-7), where you can shoot directly into the bow or stern of the vessel, making the SAP shells explode deep within the hull.
  
• Airplanes should be avoided. Instead, use secondary or anti-air guns to counter them. If desperate, HE shells will give you better results.

History

The French 203 mm/50 Modèle 1924 gun was designed in the early 1920s for the Duquesne-class cruisers. Made to comply with the Washington Naval Treaty limitations, it featured a simple construction, with a breech block that opened upwards. Initially, it fired 123.1 kg armour-piercing shells and 123.8 kg high-explosive shells. Later developments in the late 1920s introduced lighter shells, and just before the Second World War, the significantly heavier armour-piercing capped Opf (K) RC Mle 1936 was developed. To aid in identifying shell splashes during formation firing, in March 1939 a special dye was added that coloured the splashes. Duquesne used red, Tourville yellow, and Suffren used green dye.

The Modèle 1924 gun was mounted in twin turrets, each housing guns in separate cradles with individual toothed elevating arcs, allowing for independent or coupled elevation for salvo firing. The turrets allowed the guns to elevate up to +45 degrees and depress to -5 degrees, with loading conducted between +10 degrees and -5 degrees using catapult rammers. The shell rooms were located below the magazines, except for some forward magazine stowage on the same deck level as the shells. Ammunition handling involved dredger hoists and upper cage hoists, with shells transferred via swinging arms that locked to the guns for loading. While the designed firing cycle was 5-6 rounds per minute, the practical rate was somewhat less. In the mid-1930s, remote power control was added for training purposes.

This gun saw service on the Duquesne and Suffren classes, with the submarine cruiser Surcouf using the Modèle 1929, and the cruiser Algérie employing the Modèle 1931 variant. The Algérie’s guns, though similar internally to the Modèle 1924, had construction differences such as an A tube and jacket accommodating a liner with an internal diameter of 324 mm. Plans were made to equip the Saint Louis class heavy cruisers, designed in 1939, with the gun, but the outbreak of the Second World War led to the project’s cancellation before design work could be completed.

Historical shell types

Initial shells, fired with 53 kg of BM13 propellant

• OPf Mle 1927 — Mass: 123.1 kg, burst charge: 8.07 kg Mélinite, muzzle velocity: 850 m/s, maximum range of 31,400 meters
• OEA Mle 1927 — Mass: 123.82 kg, muzzle velocity: 850 m/s, maximum range of 30,000 meters

Second series of shells, lighter designs introduced in 1920s

• OPf Mle 19?? — Mass: 119.07 kg
• OEA Mle 19?? — Mass: 119.72 kg

A heavier Armour Piercing Capped shell introduced in 1936, fired with 47 kg of BM13 propellant

• OPf Mle 1936 aka Opf(K) RC Mle 1936 — Mass: 134 kg, burst charge: 8.3 kg of Mn.F.Dn (Mélinite fondue dinitronaphtaline — roughly equivalent to British Shellite which has x0.94 multiplier for TNT equivalent, giving it a TNT equivalent of 7.8 kg TNT) muzzle velocity: 850 m/s

OPf stands for Obus de Perforation (Armour-Piercing Shell), OEA stands for Obus Explosif en Acier (High-Explosive Steel Shell).

Sources

• [Wikipedia] 203mm/50 Modèle 1924 gun
• [NavWeaps] France 203 mm/50 (8”) Model 1924
• Naval Weapons of World War Two by John Campbell, page 292
• French Cruisers 1922-1956 by John Jordan & Jean Moulin, pages 48-49, 162-163
• Warship 2005 — Duquesne and Tourville: The First French Treaty Cruisers by John Jordan, page 33 (largely the same facts as in the French Cruisers 1922-1956)