During 1935 the Director of Naval Construction produced several design studies showing various alternatives for what became the King George V class battleships. One of these, designated 15C, was for a design with nine 15"/45 (38.1 cm) guns in three triple turrets. This design was considered to be one of the best proposals for these ships, but
Treaty restrictions prevented the use of guns larger than 14" (35.6 cm). For this reason, work on designs with 15 and 16 inch (38.1 and 40.6 cm) guns was discontinued and only 14 inch (35.6 cm) designs were pursued.
Construction of these new 15" (38.1 cm) guns would not have resembled the older wire-wound
15"/42 (38.1 cm) Mark I. Instead, they would have been of an "all steel" design similar to the
14"/45 (35.6 cm) Mark VII guns actually used on the King George V class.
They were to have had a new-gun bore diameter of 14.985 inches (38.06 cm) in order to reduce clearance and thus increase accuracy life with 6crh shells.
Each of these new 15"/45 (38.1 cm) guns would have been about 3 tons (3.1 mt) lighter than the old 15"/42 (38.1 cm) Mark I, even though the new guns were three calibers longer than the old ones. It must be kept in mind that weight reduction was an important consideration for all of the Treaty limited warship designs of the 1920s - 1930s.
A weight savings of 27 tons (28 mt) for nine guns, plus the accompanying reduction in ship's structure, would be considered quite significant for that reason.
It is possible that the new 15" (38.1 cm) triple mountings would have had the same interlock and other reliability problems found with the 14" (35.6 cm) mountings actually used on the King George V class battleships, as they shared similar design concepts.
The data that follows is necessarily of a sketchy nature, as little formal design work was done on this weapon and no prototypes were ever produced.