Due to the urgency of the times, the normally slow and cautious prototype and testing stages of a new gun's development were bypassed, and it was ordered straight from the drawing board.

Despite its hurried development process, the gun met all expectations and was a competitive battleship main armament throughout both World Wars.

[2] During World War II unreconstructed older battleships, with gun elevation limited to 20°, were supplied with supercharges to increase their maximum range to 29,930 yards (27,370 m) at 2,638 ft/s (804 m/s) using the Mk XVIIB or Mk XXII projectile, while HMS Vanguard could theoretically range to 37,870 yards (34,630 m) while using supercharges at a gun elevation of 30°.

[9] The BL 15-inch Mark I gun proved its effectiveness at the Battle of Jutland in 1916, scoring hits out to 19,500 yards (17,800 m), a record for naval gunnery at that time.

[10] In World War II the gun was responsible for the longest range shell-hit ever scored by one battleship on another in combat.

At the Battle of Calabria on 9 July 1940, HMS Warspite gained a hit on the Italian battleship Giulio Cesare with her first salvo at 26,400 yards (24,100 m).

Dunkerque's main 225mm armour belt was twice penetrated by 15-inch shells, which destroyed its fighting and steaming abilities.