40 mm BOFFIN  (BOFORS) A/A GUN

The Bofors 40 mm gun, is an anti-aircraft cannon designed in the 1930s by the Swedish arms manufacturer AB Bofors. It was one of the most popular medium-weight anti-aircraft systems during World War II and  used by most of the western Allies as well as some captured systems being used by the Axis powers. A small number of these weapons saw action as late as the Persian Gulf War.

These 40 mm,  Bofors anti aircraft guns were installed bertween 1946 and 1947, on top of the original twin 20 mm OERLIKON power mountings. This was an RCN innovation. The mounting operated hydraulically, with the fluid being supplied by the pumps forward of the after funnel on the Bofor deck, and aft of the helm at the Emergency Steering position. The mounting moved in response to the movement of the fire control "joystick". These guns used to have a Mark II Gun sight,  but they are missing.

The design of the gun is such that it had a very high rate of fire due to the fact that the vertical block in the breech, opened upon recoil of the gun, so that the casing was ejected almost immediately after firing. This resulted in a rate of fire of 120 rounds per minute. The rounds were loaded into the breech in "clips" of fourand by a  crew of four. They were: Trainer/Aimer, Breechworker, Layer, and Loader. The ammunition used was high explosive, and was not fused. The gun could elevate to 70 degrees, and could depress to 0 degrees which allowed it to be used against close in surface contacts which were below the arc of fire of the twin 4 inch guns. The Boffins was very useful in Korea for blowing up floating mines.

HAIDA was  fitted with the Mk VII Bofors. In Wilipedia, Mk VII is defined as "a single barreled, hydraulically powered mounting that superseded the Mark III and entered service in 1945.

AMMUNITION:

There are two known projectile types that were used with the Boffin.  One employed high explosive (HE) while the other was a practice projectile consisting of just a steel casing. As of 2014, there  was a stockpile of HE 40 mm projectiles still in DND stores. These  were leftovers from WWII. Since the practice ammunition is now exhausted, HE shells are now being used for target practice.

This is more commonly called a 40 mm Bofors anti-aircraft  gun. HAIDA has four of these single barrel guns  in total which are correctly called a Boffin. In RCN nomenclature, when a 40 mm Bofors gun was mounted on an Oerlikon power mount, it was called a Boffin. In the slang of the United Kingdom, Australia, New Zealand and South Africa, boffins are scientists, engineers, and other people who are stereotypically seen as engaged in technical or scientific research. The Boffin had a rate of fire of 120 rounds per minute and a maximum vertical height of 23,300 feet. These guns were fitted with Mk II gyro gunsights when HAIDA was in service,  but they were removed when HAIDA paid off. .

Rear view of Boffin. Click on image to enlarge.

These are the hydraulic pumps which operate the forward 40 mm Boffins These are  located midships, port and starboard. All four guns had therir own pumps.

Shelter for the forward 40 mm Boffin  gun crew. There was no such shelter for the crew of the aft guns.  With just a screen on the door, it makes one wonder how much heat was retained in the gun crew shelter.

Inside the 40 mm gun crew shelter. The bench runs full width of the shelter .

The only amenity in the gun crew shelter is this space heater. On the port side there is a box with a charger for the work boat batteries The knife switxh likely controlled the input power to the battery charger.

The Boffin as it looked while HAIDA was in service. It was a single barreled weapon , with a hydraulically powered mounting designated as Mk VC. It means Mark 5, Canadian. The arrow identifies the location of he Mk II gyro gun sight. Ii provided the lead-off angle for the fire control solution.   (Photo by Colin Blackburn)

This is an enlargement of the previous photo. Looking for a closeup  photo of  a MkII gyro gun sight. Please contact:   jerry.proc@sympatico.ca

This is only the optical portion of the the 40 mm gun sight. It could be swung out of the way if the operator wanted to control the gun with the gyro,.The gyro itself is missing. Electrically speaking, the gyro connected to the two junction boxes on the support bracket.  Click on image to enlarge.

Boffin gun crew aboard HMCS Ontario in 1949. Click on image to enlarge. So far, this is the best view of the gyro gun sight when enlarged. ( CFB Esquimalt Naval Military Museum  photo number VR 991 337 16)

The MK II gyro gun sight provided the lead-off angle for the gun based on range input from the aimer.  (Gtaphic courtesy USN)

  Reference::

1) HAIDA Docent Manual . Peter Dixon . 1999
2) https://en.wikipedia.org/wiki/Bofors_40_mm_gun
3) Colin Blackburn  <acblack(at)shaw.ca>
4) Lead-off pictorial https://www.ibiblio.org/hyperwar/USN/ref/Ordnance/GS-Mk14/index.html\
5) HMCS Ontatio Boffin photo via CFB Esquimalt Naval Military Museum
 
 

Jun 16/21