The twin 4.5-inch upper-deck mount weighed about 30 tons, roughly five tons more than the Tribal's twin 4.7-inch mounting. Its elevation ran from -5 to 80 degrees, compared with -10 to 40 degrees for the 4.7-inch mount, but its 300-degree firing arc was 20 degrees narrower. The 4.5-inch gun could reach 20,750 yards at 45 degrees, while the quoted 4.7-inch range reached 17,000 yards at 40 degrees. It could also penetrate 2.5 inches of armor from about 4,000 yards farther away. The smaller caliber therefore remained competitive in a surface action, although the upper-deck installation was hand-worked in training and elevation. Mount weight, movement, firing arc, and crew workload mattered more to the destroyer design than the small difference in caliber.
Chapter · 10:10-15:14
4.7-inch and 4.5-inch performance depended on the mount
A detailed comparison finds the 4.5-inch gun attractive in range, penetration, and elevation, but heavier and hampered by hand-worked training.