Moving a carrier island across the flight deck is more than a cosmetic alteration. Exhaust stacks and their trunking must cross different parts of the hull, which in turn changes machinery services, workshops, fuel-system connections, and internal spaces. That engineering consequence is why Sōryū and Hiryū are treated only loosely as one class. The comparison establishes their common air-group scale and 34-knot speed while noting Hiryū's greater range and roughly 1,400 tons of extra standard displacement. One topside choice can therefore propagate throughout a warship design.
Notable Point · 27:23-30:05
Why a mirrored island required a different ship
Moving Hiryū's island to port forced changes to exhaust trunking, machinery services, workshops, and internal arrangement rather than producing a simple mirror image.