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).
Future aircraft armament options, comparing various gun calibers including the Hispano.
| Identifier | ExFiles\Box 176\1\ img014 | |
| Date | 6th February 1940 | |
| -2- Rm.{William Robotham - Chief Engineer}4/MH.{M. Huckerby}6.2.40. Any new design, therefore should (1) Be able to pierce any armour plate that the enemy may reasonably be expected to use. (2) Have sufficient rate of fire and length of burst to provide an odds on chance of hitting the objective at increased range. It appeared to be universally agreed that the 20 mm. Hispano had all the hitting power necessary. Also the Spitfire carrying two Hispanos succeeded in scoring six hits out of a total of 35 rounds fired with one gun only as the other jammed. It seems probable that these 20 mm. projectiles brought the machine down. The Hispano gun, however, is very awkward to install in a turret owing to its length and the number of rounds that can be carried is very limited. It also will not operate at low temperatures. Considerable doubt was expressed as to whether the 13.2 gun was man enough for three years hence. In any case, the opinion was expressed that we should have to go into production with the Belgian 13.2 mm. which would make the adoption of another gun of similar size at a later date a somewhat questionable war-time policy. There seemed to be a feeling that a 16 mm. or 17 mm. gun would be the best bet and that, in view of the inevitable lapse of two or three years before the gun could be got into the service it would be ridiculous to handicap design by insisting on using existing ammunition. We suggest that a table should be drawn up of four or five sizes of gun between 13.2 and 20 mm. showing the number of guns and cartridges that can be carried for the same weight as the existing eight .303 Brownings and their ammunition. That the dimensions of the guns should be shown in pictorial form and also a graph made of the effect of M.V. on the dimensions of the gun and the quantity of ammunition that can be carried. At the same time the absolute maximum size of gun that can be installed in the Spitfire should be indicated. We believe with this information available a more intelligent choice of size should be possible than hitherto. Rm.{William Robotham - Chief Engineer} | ||