Description

Unusual for this size gun in that the twin turrets had the guns individually sleeved. They were also used in single casemate mountings on the carrier Bearn.

Developed from Army guns of the same caliber. Built with an autofretted A tube, liner, jacket in two lengths and breech ring. Used a Welin breech mechanism which opened upwards.

Gun Characteristics

Designation 155 mm/50 (6.1") Model 1920
Ship Class Used On Duguay-Trouin, Jean d'Arc and Bearn classes
Date Of Design 1920
Date In Service 1926
Gun Weight 8.73 tons (8.87 mt)
Gun Length oa 316.9 in (8.050 m)
Bore Length 305.1 in (7.750 m)
Rifling Length 250.5 in (6.362 m)
Grooves (about 46) about 0.059 in deep x 0.295 in (1.5 mm x 7.5 mm)
Lands about 0.120 in (3 mm)
Twist Uniform RH 1 in 22.35
Chamber Volume 2,238 in3 (36.67 dm3)
Rate Of Fire 3-5 rounds per minute 1
  • ^The expected rate of fire for the light cruisers was six rounds per minute, but three rounds per minute was the usual rate of fire. The Permanent Trials Board criticized the complicated ammunition supply system.

Ammunition

Type Bag
Projectile Types and Weights SAP: 124.6 lbs. (56.5 kg)
HE, internal nose fuze: 130.1 lbs. (59.0 kg)
HE, base fuze: 124.6 lbs. (56.5 kg)
Illum: N/A
Bursting Charge SAP: about 6.5 lbs. (2.9 kg)
HE, internal nose fuze: 12.4 lbs. (5.6 kg) picric acid
HE, base fuze (original): about 7.4 lbs. (3.3 kg) picric acid
HE, base fuze (later): about 6.5 lbs (2.9 kg) cast TNT
Projectile Length SAP: 31.5 in (80 cm)
HE: about 30.5 in (77.5 cm)
Propellant Charge 43.67 lbs. (19.81 kg) BM11 1a
Muzzle Velocity New gun with SAP: 2,854 fps (870 mps)
New gun with HE, base fuze: 2,835 fps (864 mps)
Average gun: 2,789 fps (850 mps)
Working Pressure about 19.4 tons/in2 (3,050 kg/cm2)
Approximate Barrel Life about 700 rounds
Ammunition stowage per gun Duguay-Trouin: 125 rounds 2a
Jean d'Arc: 150 rounds
Bearn: N/A
  • ^The propellant charge was in halves and was rectangular in shape.
  • ^Duguay-Trouin outfit was 1,000 HE, 60 illumination for upper turrets, no illumination for lower turrets, 40 practice rounds for upper turrets and 120 practice rounds for lower turrets.

Range

Range with different shells
Elevation 124.6 lbs. (56.5 kg) SAP Shell 124.6 lbs. (56.5 kg) HE Shell
5 degrees 9,400 yards (8,600 m) ---
10 degrees 14,220 yards (13,000 m) ---
30 degrees 24,060 yards (22,000 m) ---
40 degrees 27,340 yards (25,000 m) 28,543 yards (26,100 m)

Mount/Turret Data

Designation
  • Single Mounts
    • Bearn (8): N/A
  • Two-gun Turrets
    • Duguay-Trouin (4) and Jean d'Arc 1b (4): Model 1921
Weight Single Mount: N/A
Twin Mount: about 78.7 tons (80 mt)
Elevation -5 / +40 degrees
Elevation Rate about 6 degrees per second
Train Model 1921: -140 / +140 degrees
Others: N/A
Train Rate 6.4 degrees per second
Gun recoil Nominal: 19.7 in (50 cm)
Maximum: 21.7 in (55 cm)

Training and elevation for the two-gun turrets were electrically powered. The design of these were basically scaled-down versions of the earlier twin battleship turrets with twin dredger cage hoists running from the magazine and ammunition spaces up to a rotating working chamber. From here the ammunition was transferred into upper cage hoists which came up on the outside of each gun. Shells and charges were then manually transferred to loading trays and rammed by power. RPC for training was slated to be added to these but cancelled upon France's surrender in 1940. The gunhouses were gas tight with forced ventilation. "French Cruisers: 1922 - 1956" says that the guns proved unreliable and experienced "regular breakdowns" throughout their service lives.

The gun axes were 59 in (150 cm) apart.

  • ^The turrets on Jean d'Arc were larger and roomier so as to fit her role as a training ship.

Additional Pictures

Sources

Data from:

  • "Naval Weapons of World War Two" by John Campbell
  • Article in Warships International No. 3, 2001, "French Light Cruisers" by Jean Guigliani and Albert Moreau
  • "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

Page History

24 March 2007
Benchmark
14 August 2010
Added additional projectile weights and burster weights
28 March 2012
Updated to latest template
29 March 2013
Added information about twin turret mountings