Click on image to fire the guns.

4ingun.jpg Standing at the bow and looking aft, are HAIDA's 4 inch guns. The lower mount  is called 'A' gun and the upper mount is 'B' gun. These guns had a maximum range of 8 nautical miles.

Technically speaking, these are twin, four inch HA/LA Mk 16 gun mounts. HA means high angle and LA means low angle. For these guns, the HA was 85 degrees and the LA was -10 degrees. When HAIDA was first commissioned, she was fitted with twin, 4.7 inch guns in the 'A' and 'B' mounts. These guns could only be elevated to an angle of 30 degrees due to the ammunition tray which protruded behind the breech. This angle was sufficient when the principal adversary was other surface ships, however, the 4.7 inch gun barrel could not be elevated sufficiently to shoot at aircraft. 

Prior to her tour of duty in Korea, Haida's forward 4.7 inch guns were replaced with the dual 4 inch mounts that are seen today. When fired, a 4 inch projectile left the muzzle at 2,610 feet per second and produced a "deck thrust" in the magnitude of 60 tons when the barrel was elevated to 45 degrees. Recoil was constant but the deck thrust varied with the angle of the gun. The range of the projectile could be upwards of 8 miles, again, depending on the barrel elevation. HAIDA's gunners had to be in good physical condition in order to load the gun because a 4 inch shell weighed 66 pounds. 

For the crew below decks, the firing of the guns could be best described as "being inside a 45 gallon drum and having someone pound it on the outside with a sledge hammer". John Clark served in HMCS IROQUOIS during WWII as a stoker and also as a gunner for the 4.7 inch guns . He recalls the hardships which were suffered during a gun firing. "I served both as a member of "Y" gun crew and also hoisting ammunition to "B" gun  at different times when I was not doing my regular watch  in #2 Boiler room. We had no ear protection and of course were never previously trained in gun crew or ammunition handling  so there was no preparation for these "happenings". I lost some hearing but I can say that being in the boiler room during some actions was the noisiest and scariest I can recall. The vibrations down there were  something else. Standing directly below the forced draft fan at higher speeds brought it all right down on top of your head with the constant firing by all guns. There was no smiling by the crew in the boiler room and hearing loss was experienced for a few days after each action. Gun firing  was an experience no one looked forward to repeating. The fact that boiler rooms were pressurized seemed to make things worse". (Photo by Jerry Proc) 


The 4 inch gun was trained, elevated and fired electrically but was loaded manually. There was manual backup in case of power failure. Both barrels were driven by the same electric motor.


A 4 inch gun mount was staffed with a crew of 15 as indicated below. In addition, there were another 12 crew supplying ammunition to the guns.  The number of men in the gun crew varied depending on what the ship was doing.

In normal operation,  there were only four crew inside  a mount. They were  "riding" (inside) the mount. The Layer and Trainer  were there as  backups  in case of a failure with the Mk 63 Fire  Control System.  Two Safety crew  operated  the interlocks that interrupted power to the firing buttons should a safety infraction occur.  One such infraction would be to have a a loader standing directly behind the gun as the recoil force drove the breech some 18 inches backwards.   The interlocks also energized  the "Gun Ready" lamps on the bridge and in the Transmitting Station.

Gun Layer  Elevates the gun barrels in manual mode and becomes the Aimer in power mode. He had an electric joy stick that trained and also elevated  gun barrels.  Gun Trainer Rotates the mount to the desired bearing.
Communication/ Range Layer  He was also the Safety Officer  Breech Worker   
Breech Worker / Captain of the Mount  

Fuze Machine Operator

Fuze Machine Operator    Fuze Setter  
Fuze Setter Attaches the desired fuse to the projectile Loaders: - 3 per barrel  
Loaders: 3 per barrel Places the shell into the breech Ammunition supply   
Ammunition Supply   Safety/Rake Number  
    Officer of the Quarters  
Note that the Crew Duty table above is  applicable to the 'B' gun. only because it was the one which had the fuze setting machine. Years ago, Cmdr Bob Willson had the fuze setting machine moved from 'B' gun to the right barrel position on 'A' gun. This was dome so that visitors could see the fuze setting machine. As a result, there is no Fuze Machine Operator or Fuze Setter positions for the 'A' gun.
This is one of two 4 inch magazines aboard the ship. 'A'  magazine held 584 rounds while 'B'   magazine held 537 rounds. The 4 inch guns could fire explosive shells  or starshell. ( Photo by Jerry Proc) 

Weight of projectile: 35 pounds
Weight of Round:: 66 pounds
Muzzle velocity: 2,691 feet per second
Rate of fire: 15 rounds per minute (with fuses)
Recoil: 60 tons when the barrel was elevated to 45 degrees. (Recoil is the common term. "Deck Thrust" is the technical name for this force.
Detonator: Electric, not mechanical.

Spent shells were extracted from the breech block by an extractor mechanism and flung unto the deck where they were kicked over the side. The  crew who fed the guns obtained the rounds from the ready-use lockers.  It was then left up to other crew  to keep the ready-use lockers provisioned with rounds during action stations. There were  four ready-use lockers  for  each 4 inch mount.


There were three fuze types used by HAIDA’s 4 inch guns.

* Direct Action  Fuze.    No setting necessary because it explodes on contact with the target.
* Starshell  Fuze. They are set for time once the shell leaves the barrel..  Altitude is determined by the gun barrel elevation., For this fuze type, the barrel would be elevated  for the  desired range plus 1/2 mile or so. The intent was to illuminate the area  behind  the target.
*  VT  - Proximity Fuze. No setting necessary. The fuze explodes in the vicinity of a metallic target like an aircraft.

Here is the way time is set in a fuze. There is a small circular channel in the bullet head  which is loaded with a powder that burns a fixed distance per second.  To change the  time on the fuze, the fuze setter shortened or lengthened  the distance from the ignition point to were it reached the charge. There were tables which related time to distance on the fuze. The Fuze Setter only rotates the nose of the shell . That in turn, changes the distance inside.


When firing at surface targets, HAIDA’s gunners used a technique called “straddling”.  When a salvo lands on either side or forward/aft of a target, this indicates that the fire  control solution is correct and the next salvos may be fired without waiting for spot correction.

This ammunition hoist has now been rigged by HAIDA volunteer Marg Mathers to illustrate a 4 inch round which has just emerged from the magazine. (Photo by Jerry Proc)

An interior view of the 4 inch gun. At the right side is the fuze setting mechanism with a practice round in the cradle.   In use, were three fuze types:
1) Proximity type. The fuze triggered when the projectile is near the target (ie aircraft) 
2) Direct action 
3) Timed fuze.   (Photo by John Paszkat)
4 in gun fuse setter DSC_0045.JPG
A more detailed view of the fuze setter. This fuze setter was moved from the 'B' gun to the 'A' gun .  Click on image to enlarge. (Photo by Jerry Proc)

As part of modernization in 1950-52, HAIDA was fitted with a pair of Mark 29 gun sights. Illustrated above is the forward sight just aft of the bridge area. The other gun sight was fitted on the forward portion of the aft superstructure and controlled the 3" 50 gun. (Photo by Jerry Proc) 
An "aimer" stood in between the two counterweights and aimed at the target by using the two optical sights mounted at the top. The upper sight (black eye shroud) was used to acquire the target while the bottom one (orange eye shroud) was used for visual tracking. As the aimer tracked the target, this motion was transmitted electrically to the gun.

In order to hit a target, the gun must be fired in advance of the target's current position. This calculation is called "leadoff".  The lead angle was developed by three gyro's fitted within the sight housing. There was one gyro for each of three planes of motion. Radar (AN/SPG34) was used to determine the actual range of the target at any given moment in time. Once the target was acquired, the aimer would squeeze the lever in the red handle and "uncage" all three gyro's. Range information produced by the radar was fed in electrically and would control the distance that the gyros moved. The longer the distance, the further the gyros travelled thus developing the lead angle. The leadoff  was also affected by the speed of the target and whether it was moving left to right or right to left. Rifling in the gun barrel imparts a spin to the projectile in order to keep it from tumbling end over end, however this spin also causes it to drift slightly to the left or right depending on the direction of the rifling. At the same time, gravity is pushing the projectile downwards. Hence, all these factors need to be taken into account when developing the leadoff angle.

The AN/SPG34 antenna affixed to the 'B' mount could control  both 'A' and 'B'  mounts simultaneously. The range difference, bearing and elevation were corrected by a parallax unit in the forward AN/SPG34 compartment.

Part of this 4 inch gun crew is definitely enjoying a lighter moment after some tough target practice. (HAIDA Archives Photo 991.074.001) 

1) Jim Brewer
2) Peter Dixon - Docent Manual 1994

Aug 17/21