As a successor to the 5.25-inch RP 10 Mk I and Mk II mountings the Royal Navy intended to develop the RP 40 Mark III mounting otherwise known as the 5.25-inch 80° Electrical Hydraulic T.959. However, this project shall not be the highlight for now. Instead, I will focus on a tangential project. On the basis of replacing the hydraulic 4.5-inch Mark VI rammer and substituting it by metadyne both for elevation and ramming, an all-electric mount was conceived. This would be the 5.25-inch RP 50 Mark III star mounting otherwise known as the 5.25-inch 80° All Electric T.960 produced by Vickers-Armstrong Limited and Messrs Metropolitan-Vickers Electrical Co. Limited
Design history
Of primary importance would be compatibility of the Mk III* mounting with the Mk III. Double deck loading, with shells and casings being on different levels would be employed and the distance between the underside of rollers and upper side of the coordinate deck would be 16 feet. The guns would be 7 in 6 ft apart. The training and elevation speeds ought to have been 20° per second maximum and acceleration of 10° per second per second.
Supply of shell and cordite to the mounting was done by rotating shell and cartridge rings. These had a designed constant speed of 5° per second. The hoists consisted of two shell and one cordite hoist per gun and were either mechanically or electrically controlled by metadyne control. One of the shell hoists per pair would be provided with a fuze setter (Mk VII) as in the 4.5-inch Mk VI. Transfer to the loading tray is by hand and the chain type rammer is metadyne controlled.
A rate of fire of 16 rounds per minute with fuse setting could be achieved, or without fuse, or with 711 fuse, a rate of fire of 20 rounds per minute should have been obtainable.
The final time chart would not be ready, but the following estimates were provided.
Loading and gun rammer
0.30 seconds Press knob to release fuze setter head
1.40 seconds Lift shell from hoist into the tray
0.30 seconds Press knob to ram
0.50 seconds Ram
0.25 seconds Close breech
0.60 seconds Withdraw
Shell and Cartridge hoists
1.55 seconds Raise
1.30 seconds Lower
Particulars of rough design, 29th June, 1944:
Weight of shell: 80 lbs
No. of shells in one lift: 4
Length of lift: 50.5”
Weight of cordite case: 41 lb
No. of cases in one lift: 5
Length of lift: 52”
Weight of revolving structure: 100 tons
Weight of oscillating mass: 11 tons
Training ° per second: 20° per sec
Acceleration: 10° per sec²
Elevation ° per second: 20° per sec
Acceleration: 10° per sec²
On the 4th of July the revolving structure estimate increased to 105 tons (with a ½ inch shield). On the 7th the same month, the elevation acceleration was increased to 15° per sec². 6 Metadyne sets would be used. 1 - training set, 2 - twin sets combining shell and cordite hoists (one for each gun), 2 - twin sets for combining rammer and elevating drives (one for each gun) and 1 twin set for fuze setters. A local position was provided with joystick control.
The shell ring would weigh 8500 lb loaded (of which 5200 lb would make up the 64 shells) and the cordite ring 4700 lb respectively with 32 shells of 1280 lb.
The elevation motor had shown a maximum performance of 20°per sec and acceleration of 21° per sec². The revolving weight of 105 tons had a 8.15 ft radius of gyration and out of balance of 3.8 inches. Oscillating weight was 11 tons per gun with 5.375 ft radius of gyration. The maximum power of the metadyne motors was 156 HP for training and 12 HP for elevation.
A mock-up of the hoist was to be prepared. A trial rammer with 4.5-inch Mk VI cradle would be prepared. Proposed trials for the system were one for full load, one for endurance, one for failure of power, one for failure of interlocks and a compatibility test. It was however not seen fruitful to do an endurance test due to the mock-up nature, but the other were approved and would be carried out.
Meanwhile, the admiralty had already shown very little attention for this project which has caused numerous delays. It now had started to doubt the merits of a vertical hoist arrangement and suspended works on the Mk III and Mk III* except for the hoist.
On the 11th December 1946 the trials with the mock up would take place. However, the day prior an unfortunate accident took place. Immediate repairs were effected but only the hoist could be made operational. The loading tray had to be manually operated for the trial, at which a speed of 16 rounds per minute was achieved.
Not satisfied with this result, a number of adjustments were contemplated. The next month a test rate of 25 rounds per minute was achieved and the following month 30 rounds per minute. A new trial was planned but due to power outages at the factory this had to be postponed. By the 4th of March they had successfully trialled a delivery rate of 31 rounds per minute. This would unfortunately prove to be the last test and the mount was dismantled by the 9th of June before its last pre-disposal inspection.
Many thanks to Trainspite for his assistance in collecting the information to write this article.
(Edit: Sources are from Tyne and Wear archives, DS.VA/6/25/11 and DS.VA/6/36/14/2)
