From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Letter extract discussing the design and mounting of a 40 m.m. Naval Gun for use on fast Motor Torpedo Boats.
| Identifier | ExFiles\Box 175\1\ img003 | |
| Date | 20th December 1940 | |
| [Handwritten notes at top] Please note and return SECRET 40 m.m. NAVAL GUN. Am LH{Mr Haworth}4/DF.20.12.40. Cen EW 17/1/41 I give you below an extract from a letter I have had from Mr. Jack Thornycroft - "Dear Mr. Haworth, Rolls-Royce Cannon. I am afraid I should have acknowledged your letter but we have been considering the design and I wanted to be able to make some useful comments. What we have in mind for use on fast M.T.B.s is an automatic not a hand loaded cannon with single shots, a 1.5 or 2-pounder automatic gun as we think it is highly desirable to get in a burst for a few seconds when the gun can be brought on the target. We believe that for night work a fixed gun is the right answer. The gun would normally be placed on the deck forward of the steering shelter where there is considerable vibration and where automatic loading with a belt, clip or drum has many advantages over hand loading, in fact we do not think the latter is really practical when fighting the boat in anything but dead calm weather. When not in use as a fixed gun, we are of the opinion that for anti-aircraft firing a maximum elevation of 85° is desirable. Your weights are certainly very satisfactory, but we can see considerable difficulty for the gunner in getting down to his job at full elevation with the mounting shown on your drawing A.B.2120. This appears to be due to having the trunnion on the centre of gravity of the gun. In the Bofors gun the trunnion is mounted well behind the centre of gravity with spring control to take up the muzzle preponderance in weight. This, together with a 45° prismatic sight, would make it easier for the gunner to handle the gun at full elevation and looking down 45° in the sight when the gun is horizontal is not an objection provided the eyepiece is at the correct height above the deck. We are enclosing a table giving comparative particulars of a V.A. Bofors and Rolls-Royce gun. We do not think that either of the first two have endeavoured to produce a very light mounting and both provide seats for the two operators, gun layers and trainers which, if eliminated, would reduce weight. Unfortunately, certain details of Bofors gun are not available. Reverting to the fixed gun proposal referred to above, have you any schemes of different types of mounting ? ---------------------continued- | ||