Royal navy A.A.gunnery.

[starling]

Hey guys,a quite fascinating thread.Starling.

 

[Juha]

Hello
on the sinking of HMS Mashona on 28 May 41. It was sunk by I./KG 77, so by Ju 88s, normally a full Gruppe attacking formation consistedof 27 bombers.

Juha

 

[Juha]

On 2pdr vs 40mm Bofors
From Britain 2-pdr [4 cm/39 (1.575")] Mark VIII
"As originally introduced, this was a recoil operated, "controlled" (partially-automatic) weapon which used a manually turned crank to operate the firing gear in the quadruple and octuple mountings (see note below for a further explanation). In 1939 the octuple mountings design was changed to allow fully automatic firing but this was not extended to the quadruple mountings which were only produced in controlled versions throughout the war. However, the quadruple mountings did replace the crank-turning crewmember with an electric motor sometime during the war.
A higher velocity projectile was introduced in 1938 and this required a different breech mechanism and other changes to the firing gear. However, guns firing only the older low-velocity projectiles were still manufactured throughout World War II. High velocity and low velocity ammunition was not interchangeable. There were also several other gun variations, as shown in the data tables below. It should be noted that standardization was never a high priority in British ordnance thinking prior to the 1950s.
The internal gun mechanisms were very complex and required much care and skilled maintenance to keep them in working condition. Jams and stoppages were frequent, although the linked ammunition proved to be more reliable in service than the older belt-fed guns."

And from Sweden, Britain, USA, Germany and Japan Bofors 40 mm/56 (1.57") Model 1936
"The British considered the Bofors to be at least twice as effective as their own 2-pdr against torpedo bombers, but not much better than that weapon against kamikazes."

And the RoFs, water cooled Bofors 120rpm, automatic 2pdr 115rpg and "controlled", that means quad, 2pdr 96-98 rpm

Juha

BTW the Finnish Navy got its first water-cooled 40mm Bofors guns during winter 40-41, they had been ordered in 1938, they replaced the older 2pdr guns on our coastal battleships (3900t, 4x10" + 8x4.1" + 4x2pdr/later4x40mm Bofors + 4 - 8x20mm Madsen)

 

[parsifal]

Finns reckoned they shot down 128 russian a/c using their copies of the bofors. they claim that this equated to 392 rpk....pretty good shooting if correct. USN a the end of the war reckoned average 40mm expenditre was 550-600 rpk. i saw the other night one site claim the 2pdrs expended 2300 rpk....of course no referenced material to verify.

 

[RCAFson]

On 2pdr vs 40mm Bofors
From Britain 2-pdr [4 cm/39 (1.575")] Mark VIII
"

Navweaps has the MV wrong, they state LV/HV =1920/2300fps but the new gun MV = 2040/2400fps.

 

[fastmongrel]

Navweaps has the MV wrong, they state LV/HV =1920/2300fps but the new gun MV = 2040/2400fps.

The RN usually quoted velocity after a certain percentage of the barrel life had been used which varied from gun type to gun type.

 

[Glider]

Both the US and the British were able to examine Dutch twin 40mm stabilized mountings in the summer of 1940. The Hazemeyer fire control system. In some cases Dutch ships had their 40mm guns/mountings removed for study and replaced by 2pdr mountings.

The Hazemeyer mounting with twin 40mm was produced for RN destroyers in the late war replacing the quad 2pd. It also had its own radar rangefinder and analogue computer. It was very accurate and guess what very unreliable an idea ahead of its time

 

[parsifal]

what were its reliability problems?

 

[fastmongrel]

what were its reliability problems?

From Navalweapons site Sweden, Britain, USA, Germany and Japan Bofors 40 mm/56 (1.57") Model 1936

The Mark IV twin mounting was derived from the Hazemeyer triaxial mounting which had its origins in the 1940 arrival in Britain of the Dutch minelayer Willem van der Zaan. The Mark IV was a self-contained twin mounting that had its own rangefinder, radar and analog computer on the mount. This mounting used Mark IV water-cooled guns and utilized a track and pinion system for elevating and training, powered via a Ward-Leonard system for automatic target tracking. The Mark IV was probably too advanced for its day and proved to be somewhat delicate for use on destroyers and sloops. The later STAAG and Buster designs were more robust, but very much heavier. According to service notes, the Mark IV was apparently used more often in manual mode than in power mode. Elevation was -10 to +90 degrees with cross-level of +/- 14 degrees with control cutting out at +/- 12 degrees. Maximum elevating speed was 25 degrees per second with the manually controlled joystick, but training and elevation control via automatic control was limited to little more than 10 degrees per second. Weight was 7.05 tons (7.16 mt). The later Mark IV* mounting differed in details of the controls and gyros. The following description taken from "Destroyer Weapons of World War 2" is of interest:

'The 7-ton "Haslemere," as it was generally known, was a brilliant concept, but unfortunately it needed more advanced technology than then existed. It cannot claim to have been the most popular of weapons but at least it provided a little light relief on occasions. When stationary in the "power-off" mode during maintenance, a combination of training, depression and cross-roll made it look for all the world as though it was about to fall off its gundeck. Observations like "I see the Haslemere is ill again" were common.'

 

[Shortround6]

All true but it does show that the RN was looking at other options besides the 2pdr, the trouble is finding the fine line between what is possible in the lab/on the test range and what is possible/reliable in the Norwegian/Barents sea or South Pacific weeks if not months out of dockyard is a hard thing to find.

 

[Glider]

I cannot find the quote now but vibration from the gun was a problem. The guns, radar, rangefinder and computer were all on the same mounting and the vibration of the gun firing could cause problems. Generally speaking and there are a number of grey areas here, the UK had more sophisticated mountings for their 20mm and 40mm guns. Their ships were a lot smaller than USN destroyers, deck space was less and they had to make the most of what space there was

 

[parsifal]

I always believed Hazemeyer and other triaxial mounts were a big step forward. That and the US type directors. Now Im not as sure.....any comments?

 

[Glider]

I odn't doubt for a moment that they were a significant step forward but the Hazemeyer by trying to do everything on one mount was a step to far for the technology of the time. As I said it was an improvement on the quad 2 pd and some of the crews loved it but it took a lot of TLC to keep going. After all the RN could easily have switched back to the 2pd.

 

[RCAFson]

Here's an interesting excerpt, showing that RN AA could be very effective, under the right circumstances:

Saturday 20th September, Two bombing attacks took place on the Convoy. During the first attack bombs were dropped over the convoy at some distance from "Parramatta" and one merchant ship was hit and damaged, although she subsequently reached Aden afloat with assistance from various ships. The Escort engaged the planes without visible results. The second attack took place during the first dog watch. The five Italian planes, inexplicably gave H.M.S. "Auckland" and myself considerable warning by dropping several bombs some miles away before attacking. The remainder of the bombs (about 30) were aimed with obvious intention of attacking the Convoy, but they released early, and the entire outfit fell around "Parramatta". The ship, then nearly stopped getting in the mine-sweeps, was not struck, although there were several near misses. Although splinters flew over us there there were no casualties, and the minesweeping party aft calmly continued to get in the sweeps with the after gun firing over their heads and bombs dropping close around them. The Italian planes continued over the Convoy at approximately 14,000 ft and gave H.M.S "Auckland" and myself an unrivalled opportunity for steady firing for some minutes. Two of the aircraft appeared to drop out of formation, one going into a spin. It has been subsequently ascertained that not one of the five aircraft reached home, in fact we had a one hundred per cent success.[10]
Fuze Keeping Clock - Wikipedia, the free encyclopedia

10)http://www.awm.gov.au/collection/records/awm78/290/awm78-290-1.pdf

 

[Juha]

Hello RCAFson
In reality only one S 79 was slightly damaged by AA. Italians on their part claimed hits on two ships. Typical cases of optimistic reporting. Usually combat reports are reliable on own losses but optimistic on losses inflicted to enemy forces.

Juha

 

[RCAFson]

Hello RCAFson
In reality only one S 79 was slightly damaged by AA. Italians on their part claimed hits on two ships. Typical cases of optimistic reporting. Usually combat reports are reliable on own losses but optimistic on losses inflicted to enemy forces.

Juha

OK thanks. Where did you read that?

 

[Juha]

OK thanks. Where did you read that?

From Chris Shores' Dust Clouds in The Middle East p. 61.

Juha

 

[RCAFson]

Does Shores mention both attacks that day?

 

[Juha]

Hello RCAFson
Shores only writes:"...S79s again attacked the Red Sea convoy, claiming hits on two ships..."(they had attacked the same convoy on 19 June) but it is difficult to believe that he has missed a loss of 5 S79s, after all there were only 12 S79s in the bombing units operating in Italian East Africa in June 40 (+ 4 in reserve) and 27 on 1 Jan 41. And usually he mentioned even light damages suffered, after all fighting in East Africa was a shoestring war.

Juha

 

[starling]

Thankyou ,starling.