The F2, F3, and Nelson concepts carried broadly comparable armor weights, while Nelson's hull was about 750 tons heavier because of its greater subdivision. Their protection was distributed differently: F3 had a uniform 12-inch belt, while Nelson had 14 inches over the magazines and 13 over the machinery. F3's armament weighed about 1,550 tons less, matching the increase from Nelson's 2,550-ton machinery plant to F3's 4,100-ton plant. That machinery raised the proposed output from 45,000 to 96,000 shaft horsepower and the speed from about 23 to 28.5 knots. F2 paired six 15-inch guns with 112,000 shaft horsepower for still greater speed. F2 and F3 remain battlecruisers in this classification because of their subdivision, despite armor coverage approaching that of a battleship.
Chapter · 19:43-28:30
F2 and F3 show how armament weight bought Nelson's missing speed
Comparing weights and machinery suggests that substituting nine 15-inch guns for Nelson's 16-inch battery could fund roughly 28-knot performance without abandoning heavy protection.