The 4.7-inch 45-calibre gun already used separate ammunition, a semi-automatic sliding breech, hydropneumatic recoil, and a rate of about fifteen rounds per minute. Its historical mounts stopped around 55 degrees, so the central design task is finding another 25 degrees of elevation while retaining useful depression for surface action. A redesigned shell could exploit the slightly larger 120 mm bore and approach the anti-aircraft performance of the 4.5-inch weapon without sacrificing muzzle velocity. The comparison supports a credible general-purpose gun with an estimated ceiling around 41,000 feet. Shell design and mounting changes remain substantial engineering work.
Chapter · 12:26-18:44
The performance case for a high-angle 4.7-inch gun
A direct comparison of shell weight, rate of fire, muzzle velocity, elevation, and ceiling shows why the familiar destroyer gun could plausibly become a heavy anti-aircraft weapon.