Similar silhouettes conceal materially different ships. Implacable had a fourth turbine, two extra boilers, a fourth shaft, a longer and higher hull, and a second hangar level. She also carried more aircraft weapons and stores, more personnel, and more room for flag and command functions. Those additions required different framing and machinery arrangements, making the class more than a stretched Illustrious. Their common appearance reflects two designs developed from the same broader armored-carrier study.
Notable Point · 26:28-29:33
Implacable versus Illustrious capacity
The comparison shows that Implacable's resemblance to Illustrious concealed a different internal arrangement, machinery plant, and operational capacity.