Capital-ship types sit on a spectrum rather than in three rigid boxes. A two-word battle cruiser such as Invincible has cruiser-level subdivision and limited armor coverage, while a one-word battlecruiser carries broader protection and a fast battleship retains battleship-level coverage. Thickness alone is not decisive because a very heavy plate over a small area leaves the rest of the ship exposed. Kongō began on the battlecruiser side of that spectrum, and later modernization has to be judged by how much protection and subdivision it added.
Notable Point · 29:11-32:07
Where Kongō sits between battlecruiser and fast battleship
A design comparison places Kongō on a spectrum defined by armor coverage and subdivision rather than treating speed as a complete classification rule.