Blucher's guns keep her outside the battlecruiser category

Blucher's 8.3-inch battery makes her a large armoured cruiser rather than a battlecruiser. The decisive criterion here is whether a cruiser carries guns comparable to contemporary battleships already in service, rather than the cruiser's size or speed. HMS Tiger still qualifies with 13.5-inch guns even though the Queen Elizabeth class carried 15-inch weapons, because the contemporary Iron Duke class also used 13.5-inch guns. Blucher fails that test because an 8.3-inch gun was below battleship calibre in her era. The distinction explains why sending her into the same fight as true battlecruisers created such a severe mismatch.