British Cruisers: Two World Wars and After

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dunmunro
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British Cruisers: Two World Wars and After

Post by dunmunro » Fri Mar 25, 2011 7:32 am

I have been pouring over Norman Friedman's new book, British Cruisers: Two World Wars and After and I have to say that this book is a real winner. It's 432 pages are densely packed with information about ship's designs, proposed designs and refits along with interesting comments and data about RN technology. I can most heartily recommend it. However, I did notice a small but serious error regarding the USN Mk37 and the RN's HACS, where Friedman states that Mk37 used gyros to measure aircraft speed and range rates. This is quite incorrect and it was not until 1942 and the Mk 14 gun sight and the USN Mk 56 GFCS of 1945 that the USN used gyros to directly measure aircraft movement. The RN pioneered this technique with the Mk IV pom-pom director, and the HACS IV GB HADT, both of which appeared in 1940.

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Re: British Cruisers: Two World Wars and After

Post by Keith Enge » Fri Mar 25, 2011 11:35 pm

Wasn't the Mark IV the Hazemeyer mount that the British copied from the Dutch after the minelayer Willem van der Zaan escaped to England? If so, that mount, according to Campbell, was first issued to Whimbrel in November 1942.

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Re: British Cruisers: Two World Wars and After

Post by dunmunro » Sat Mar 26, 2011 4:34 am

Keith Enge wrote:Wasn't the Mark IV the Hazemeyer mount that the British copied from the Dutch after the minelayer Willem van der Zaan escaped to England? If so, that mount, according to Campbell, was first issued to Whimbrel in November 1942.
No, the hazemeyer mounting was a triaxial twin barrel bofors gun mount, that first appeared in late 1942 - this has nothing to do with fire control. The Mk IV Pom-pom director appeared in 1940 (See Campbell, page 20). The Mk IV HACS IVGB HADT first appeared in 1940, also and is described by Campbell on page 17-18. There is a drawing of HACS III and Type 285 radar on page 16 of Campbell.

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marcelo_malara
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Re: British Cruisers: Two World Wars and After

Post by marcelo_malara » Tue Apr 05, 2011 4:37 pm

There is a good description of the Mk-37 system in "Sumner-Gearing Class Destroyers" (Sumrall). The Mk-37 sent the range (obtained by radar) and target´s bearing to the Computer Mk-1, so it could calculate the speed and course of the target and predict its future position. As the computer used a stable element, which was a gyro in itself, you can loosely say that the gyro had a part in the job. But otherwise you are correct, the Mk-14 was the gyro-based one.

I have British Destroyers (Friedman) and I must admit that the author has vastly improved its writting from what I have previously read. But it is not without its faults. For examble, he gives a British ship sunk in Malvinas/Falklands by unguided rockets, where no such weapon was in use and it was sunk by bombs.

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Re: British Cruisers: Two World Wars and After

Post by dunmunro » Thu Apr 07, 2011 7:14 pm

Friedman describes HACS 1 and on page 237 states: "...that there was no attempt to measure target motion using gyros, as in US systems such as Mark 37." HACS 1 appeared in 1930 and Mk37 in 1941, so comparing the two systems is a bit strange to begin with, but in fact even HACS1 used a "stable element", namely a liquid mercury pendulum, which fed roll information to the computer which then used that information to correct the layer/trainer's elevation/deflection data from the unstabilized director sights, so that the computer was predicting target motion based upon the true positions of the aircraft. Mk37 used gyros to stabilize the sights directly, but the gyros were not involved in target motion prediction. HACSIII, in 1937, introduced a Gyro Level Corrector to replace the liquid pendulum and later versions used the GLC to stabilize the sights in elevation. HACS IV, from 1939, used GLC stabilized sights in all versions, while HACSIV GB, from 1940, used dual axis stabilization for elevation and deflection and added the Gyro Rate Unit, to directly measure aircraft speed and direction and passed this info directly to the computer via GRUB, so that by 1941 the RN had a broadly comparable unit to the USN's MK37, in terms of AA FC, in that all aspects of target motion were based upon measured, or tachymetric, data. The Mk33/37 system had the advantage that it used remote power control (automatic gun drives in USN parlance) right from the start, where HACS only slowly introduced RPC from 1941/42 onward. However HACS/GRU could form a solution much faster than Mk37, especially when that system was used in full tachymetric mode, when it often took 30 seconds or longer to form a FC solution.

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Re: British Cruisers: Two World Wars and After

Post by marcelo_malara » Thu Apr 07, 2011 11:14 pm

May be he referred to the Mk 33 and it is a typo error.

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Re: British Cruisers: Two World Wars and After

Post by dunmunro » Fri Apr 08, 2011 2:04 am

marcelo_malara wrote:May be he referred to the Mk 33 and it is a typo error.
The USN equivalent to HACS 1 was Mk 19, even Mk33 did not appear until ~1937, and it is equivalent to HACS III in terms of development.

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Re: British Cruisers: Two World Wars and After

Post by marcelo_malara » Fri Apr 08, 2011 3:52 pm

So there is no excuse to the error!!!

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