The title of the World War II cruiser with the thickest armor generally goes to the Russian heavy cruiser Kronshtadt—though it was never completed. For operational ships, Japan's Tone-class and Mogami-class, Germany's Admiral Hipper-class, and the U.S. Navy's Baltimore-class heavy cruisers stand out among wartime designs.
Key Contenders
1. Unfinished Soviet Kronshtadt-class
Armor Thickness: Designed with a belt armor of up to 230 mm (9.1 inches).
Details: These ships were intended to blur the line between cruisers and battlecruisers, carrying both cruiser armament and battleship-level protection. Their construction was never completed due to World War II.
2. Admiral Hipper-class (Germany)
Armor Thickness: 70–80 mm (belt), with citadel armor up to 105 mm.
Details: Among Germany’s heavy cruisers, Prinz Eugen is most famous for surviving major naval engagements, thanks in part to its robust armor scheme, which emphasized protection over firepower.
3. Baltimore-class (United States)
Armor Thickness: 152 mm (6 inches) belt.
Details: These U.S. heavy cruisers were designed for powerful AA defense and as escorts for carrier groups. While not the most heavily armored, their protection was well-balanced for their mission profiles.
4. Tone-class (Japan)
Armor Thickness: 140 mm (5.5 inches) belt.
Details: Japanese cruiser design emphasized speed and offensive firepower over armor, but the Tone-class was relatively well-protected for a Japanese cruiser.
5. Mogami-class (Japan)
Armor Thickness: Up to 140 mm belt.
Details: These heavy cruisers were upgraded from light cruiser configurations, featuring good speed and firepower with improved protection after early design flaws were addressed.