Used only on La Argentina, this was a loose barrel AA gun with a horizontally sliding breech block.

This weapon is described as having a vertically sliding breech block in "Naval Weapons of World War Two" but the photograph below shows quite clearly that it is horizontally sliding.

Gun Characteristics

Designation 4"/50 (10.2 cm) QF Vickers Armstrong Mark P
Ship Class Used On La Argentina
Date Of Design About 1935
Date In Service 1937
Gun Weight 2.175 tons (2.210 mt) including BM
Gun Length oa 210.75 in (5.353 m)
Bore Length 200.0 in (5.080 m)
Rifling Length 166.807 in (4.347 m)
Grooves (32) 0.039 x 0.270 in (1.00 x 6.86 mm)
Lands 0.123 in (3.12 mm)
Twist Uniform RH 1 in 30
Chamber Volume 499.8 in3 (8.19 dm3)
Rate Of Fire 10 - 12 rounds per minute (?)


Type Fixed
Weight of Complete Round 57.75 lbs. (25.2 kg)
Projectile Types and Weights HE: 31 lbs. (14.1 kg)
Bursting Charge N/A
Projectile Length N/A
Propellant Charge N/A
Muzzle Velocity 3,000 fps (914 mps) 1
Working Pressure 19.0 tons/in2 (2,990 kg/cm2)
Approximate Barrel Life N/A
Ammunition stowage per gun N/A
  • ^With such a high muzzle velocity, I would suspect that barrel life was rather short.


Range with 31 lbs. (14.1 kg) HE Shell
Elevation Distance
45 degrees 19,900 yards (18,200 m)
AA Ceiling @ 90 degrees 37,400 feet (11,400 m)

Mount/Turret Data

Designation Single Mounts: La Argentina (4)
Weight N/A
Elevation -5 / +90 degrees
Elevation Rate 14 degrees per second 1a
Train About -50 to +50 degrees
Train Rate 16 degrees per second 1a
Gun recoil N/A
  • ^1.11.2The elevation and train rate speeds given above assume that RPC was fitted to these mountings, but it is not known if this equipment was actually installed.

Additional Pictures


"Naval Weapons of World War Two" by John Campbell
"Cruisers of World War Two" by M.J. Whitley

Page History

05 April 2008 - Benchmark
05 May 2021 - Converted to HTML 5 format