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) 

This is one of two 4 inch magazines aboard the ship. 'A'  magazine held 584 rounds while 'B'   magazine held 537 rounds. (Photo by Jerry Proc) 

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 fuse setting mechanism with a practice round in the cradle. (Photo by John Paszkat)

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.

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

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Jan 9/14