The Mark X offered dependable barrel life, while the longer Mark XI wore out too quickly to be the preferred choice. The Mark XII restored barrel life and offered better range, but its availability for a 1912 order remains an inference from an approximate 1913 date and earlier development work. Its recorded ranges came from monitor mountings elevated to 40 degrees. Those results suggest useful fire out to about 18,000 yards in a cruiser installation, against expected cruiser engagements below 13,000 yards. The comparison uses about two rounds per minute, although the Mark XII's rate and barrel-life evidence also come from monitor conditions. A cruiser mounting's performance would therefore need to be estimated. Lighter ammunition and turret machinery than a 12-inch weapon would help keep the proposed ship affordable.
Chapter · 22:00-31:22
The Mark XII's promise and the limits of monitor gun trials
The Mark XII offers a plausible balance of range, barrel life, and installation weight, with its 1912 availability and cruiser performance inferred from limited evidence.