A new design used on France's Treaty Cruisers in twin turrets and in a special lightweight twin mounting on the submarine Surcouf.

This weapon was of simple construction with a thick autofretted A tube, shrunk jacket and breech ring. The Welin breech-block opened upwards.

Actual bore diameter was 20.30 cm (7.992").

A Note on Sources: Many references state that Algérie used a longer 55 caliber gun, but recent research by John Jordan and Jean Moulin in their "French Cruisers: 1922 - 1956" has determined that she carried the same 50 caliber guns as did the older cruisers.

• ^Planned rate of fire for cruisers was 5 - 6 rounds per minute, but in practice it was closer to the above values.

• ^

  Actual French designations

  SAPCBC M1927	OPf Mle 1927
  APC M1936	Opf(K) RC Mle 1936
  HE M1927	OEA Mle 1927

• ^Besides the projectiles listed above, there appears to have been two others for which little is known:
     OPf Mle 19?? - 262.50 lbs. (119.07 kg)
     OEA Mle 19?? - 262.94 lbs. (119.72 kg)
• ^SAPCBC M1927 had a hardened shell cap and a ballistic cap which might be described as an APC shell type. However, the burster weight for this projectile was about 6.5% of the total weight, which is much more than that for an APC. For that reason, I believe that this projectile is better described as a SAPCBC type.
• ^APC M1936 added a dye bag in March 1939. Colors were assigned as follows:

  Ship	Color
  Duquesne	red
  Tourville	yellow
  Suffren	green
  Others	N/A

• ^The propellant charge was in halves. Each cartridge used a 1.65 lbs. (0.750 kg) black powder igniter.
• ^It is not known when the Later charge was introduced, but it may have been when the APC M1936 entered service. This heavier projectile may have created too high of a barrel pressure with the original charge.
• ^At least the Suffren class and probably the others had a peacetime outfit of 120 rounds per gun but had enough magazine space for 150 rounds per gun.

The range for the SAPCBC M1927 and HE M1927 when using the Original charge [MV of 3,936 fps (895 mps)] is not known.

• ^The cruiser mountings used catapult rammers cocked by the recoil forces to load projectiles while propellant charges were loaded by hand. Guns were individually sleeved. Each gun used a 30 hp elevating electric motor and the guns could be coupled together. Turrets used a 22.5 hp electric training motor with hydraulic drive and were equipped for RPC for training during the mid-1930s refits. However, RPC for elevation was not added. Shell rooms were generally below the magazines, except for some bow mountings which were on the same level. Dredger hoists from the magazines ran up to a working chamber where ammunition was transferred to the upper cage hoists which each carried a projectile and two half charges. Upper hoists ended on the outside of the guns and the projectiles were transferred by swinging arms which were locked to the guns for loading. RPC for training was added during the 1930s. The Model 1924 was considered successful and was used on all cruisers except Algérie. Her M1931 turrets were similar to the previous M1924 but had more powerful training motors to handle the increased armor weight.
• ^Model 1924 and Model 1931 gun axes were 74 in (188 cm) apart while those in Model 1929 were about 104 in (264 cm) apart.
• ^In 1939 the French started designing new cruisers that were intended to replace the Duguay-Trouin class. The preliminary design was known as "C5" and was for a 10,000 ton Treaty Cruiser similar to Algérie but having nine 203 mm (8") guns in three turrets. The start of the war ended all treaty restrictions and in early 1940 a more ambitious nine-gun design known as "St. Louis" was under consideration. Little more than some preliminary sketches for a ship of around 15,000 tons were completed before the June 1940 Armistice halted all work.
• ^The Model 1929 used on the submarine Surcouf could open fire within 2.5 minutes after she surfaced. Guns were not individually sleeved and the turret was water-tight.
• ^

  The weight differences for the cruiser turrets were mainly due to armor thickness, which "French Cruisers: 1922 - 1956" lists as follows:

  Model 1924 - Duquesne and Suffren classes

  Front	1.2 in (3 cm)
  Sides	1.2 in (3 cm)
  Roof	1.2 in (3 cm)
  Rear	1.2 in (3 cm)

  This protection was provided by riveting two 0.6 in (1.5 cm) HT plates together.

  Model 1931 - Algérie

  Front	3.9 in (10 cm)
  Sides	2.8 in (7 cm)
  Roof	2.8 in (7 cm)
  Rear	1.96 - 3.3 in (5 - 8.5 cm)
  Floor	1.6 in (4 cm)

"Warship Volume VII" article by Francis J. Allen
"Naval Weapons of World War Two" by John Campbell
"French Cruisers: 1922 - 1956" by John Jordan and Jean Moulin
"Navies of the Second World War - The French Navy" by Henri le Masson
"Cruisers of World War Two" by M.J. Whitley
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Ministère de la défense
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Special help from John Jordan - Email conversation of 14 February 2022

22 July 2007 - Benchmark
03 March 2012 - Updated to latest template
28 March 2013 - Added photographs of Foch and Algérie
06 April 2013 - Added projectile and mounting information, notes on Algérie and note on 1939-1940 designs
08 January 2016 - Corrected training angles for Surcouf. Redid side view photograph of Surcouf and added new photograph of Surcouf showing the turret training.
11 November 2020 - Updated to HTML 5 format
12 March 2022 - Added sketch of 203 mm SAPCBC projectile, added details to ammunition table
17 August 2022 - Added ammunition RPG for cruisers, added details to turret design
13 May 2023 - Added additional details in note for SAPCBC M1927
04 August 2024 - Added sketches of OPf(k) 1936 ammunition