Why are G3 and Iowa classed differently when both look like fast capital ships?
Short answerIowa was expected to fight other battleships in the battle line. G3 remained on the battlecruiser side of this classification despite its strong subdivision and its relationship to Tiger's more densely constructed design.
NotesBattlecruiser and fast-battleship labels occupy positions on a spectrum defined by expected opponents and the extent of their protection. A battlecruiser trades protection for speed in scouting, commerce warfare, and fleet screening, while a fast battleship is expected to fight other battleships. Dry docks, machinery space, and national strategy shape that compromise, so gun calibre or belt thickness alone cannot settle the classification. Tiger's dense construction and subdivision bring it closer to the fast-battleship end of this spectrum than Renown, Repulse, or Hood. G3 follows Tiger's development stream more closely than Hood's, while Iowa was expected to join the battle line and fight peer battleships.