This weapon had an interesting history. It was originally designed to replace the spigot mortar used on Churchill AVRE tanks. However, the Army selected a 6.5" (16.5 cm) cannon in its place and development of this short-barrel 4.5" (11.4 cm) gun was halted. Then, in May 1944, the Navy was looking for a more powerful gun than the 6-pdr 7cwt in order to increase the hitting power of the MTBs of the Coastal Forces. Eighteen each of the 4.5" 8cwt gun and the Army's 95 mm (3.74") howitzer were ordered and comparison tests were performed at Shoeburyness against targets representing R-boats, sampans, armored barges and merchant ships. In the official report, the Navy concluded that the 4.5" (11.4 cm) gun was clearly superior and it was selected for further development.

Unfortunately, the very low muzzle velocity of this gun gave it a rather short range, about half of what was really desired, and shipboard firing trials with it were not very successful. Nonetheless, it was approved, although it did not enter service until long after the end of the war, and was used on MTBs and MGBs for the next fifteen years.

Constructed of barrel, removable breech ring and vertical sliding breech block with semi-automatic operation. The original naval order was for three prototypes and 106 guns. In September 1945 the Navy agreed to accept all 98 guns that had been finished, even though the requirement at that time was only 60 guns. A total of 36 Mark I mountings were actually completed along with a very few Mark II mountings.

Postwar, the British tried to develop a stabilized mounting for this weapon, designated as CFS-1 (Coastal Forces System Mark 1). The weight of this mounting grew alarmingly with "improvements" and did not see service use.

Actual bore length was 18.88 calibers. All British 4.5" naval guns have an actual bore diameter of 4.45" (11.3 cm).

Nomenclature note: CFS-2 was a stabilized mounting utilizing the 20-pdr (3.28" or 83.4 mm) Centurion tank gun. Although lighter than the CFS-1, it was still too heavy for coastal craft and did not see service use. Prototype was on Bold Pioneer, a photograph of which makes one wonder how the ship could be steered, as the gunhouse blocks much of the forward view.

Gun Characteristics

Designation 4.5"/19 (11.4 cm) 8cwt QF Mark I
Ship Class Used On MTB 5091, 520, 5281, 530, 538, 790, 2014, 2017, 5007 and 5008
Date Of Design 1944
Date In Service 1946
Gun Weight 0.400 tons (0.406 mt)
Gun Length oa 89.1 in (2.262 m)
Bore Length 84.0 in (2.134 m)
Rifling Length 73.49 in (1.867 m)
Grooves N/A
Lands N/A
Twist Uniform RH 1 in 25
Chamber Volume 137.5 in3 (2.253 dm3)
Rate Of Fire 10 rounds per minute cyclic
  • ^1.11.2First entered service on MTB 509 and 528 in April 1946.


Type Fixed
Weight of Complete Round N/A
Projectile Types and Weights HE: 22 lbs. (10 kg)
Bursting Charge 5.5 lbs. (2.5 kg)
Projectile Length 19 in (48 cm)
Propellant Charge 1.148 lbs. (0.52 kg) NQ/R 014 x 048
Muzzle Velocity 1,500 fps (457 mps)
Working Pressure N/A
Approximate Barrel Life N/A
Ammunition stowage per gun N/A 1a

Cartridge cases for this weapon were apparently cut-down 3.7" (9.4 cm) AA cases.

  • ^Mark I mounting carried seven ready rounds.


Range with 22 lbs. (10 kg) HE
Elevation Distance
10 degrees 3,300 yards (3,020 m)

Although the Mark I mounting could elevate to +12 degrees, the gun was only sighted to 9 degrees 58 minutes.

Mount/Turret Data

  • Single Mountings
    • MTBs (1) and MGBs (2): Mark I 1b
    • Prototypes: Mark II 2b
    • Stabilized: CFS-1
Weight Mark I: 1.738 tons (1.766 mt)
Mark II: N/A
CFS-1: N/A
Elevation Mark I: -10 / +12 degrees
Mark II: -10 (?) / + 30 degrees
CFS-1: N/A
Elevation Rate N/A
Train about +150 / -150 degrees
Train Rate Mark I: 25 to 30 degrees per second
Mark II: Manually operated, only
CFS-1: N/A
Gun recoil Mark I: 29 to 30 in (74 to 76 cm) 3b
Mark II: N/A
CFS-1: N/A
  • ^The Mark I was developed from a powered twin Oerlikon mounting and was hydraulically powered from a pump driven by the auxiliary or main engines. This conversion proved to be underpowered when faced with the much heavier 4.5" (11.4 cm) gun barrel and was found to be unable to ensure proper tracking in rough weather. In an emergency, a manual pump located on the mounting could be used. This mounting included a launcher for firing illumination rockets.
  • ^The Mark II was a lighter, manually operated mounting that saw limited service use.
  • ^Note the long recoil stroke for the Mark I, which reduced the blow to the lightly constructed MTBs.


Data from:

  • "Naval Weapons of World War Two" and "British Naval Guns 1880-1945 No 16" article in "Warship Volume IX" both by John Campbell
  • "The Postwar Naval Revolution" by Norman Friedman
  • "Notes and Comments on the 4.5in, 8cwt Gun" article by Geoffrey Hudson in "Warship Volume VI"
  • "Anatomy of the Ship: Fairmile 'D' Motor Torpedo Boat" by John Lambert
  • "The Sad Story of the 4.5in 8cwt Gun"" article by Antony Preston in "Warship Volume V

Special help by Shane Rogers

Page History

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