Montana Class Battleship - Armor

Armor

Aside from its firepower, a battleship's defining feature is its armor. The exact design and placement of the armor, inextricably linked with the ship's stability and performance, is a complex science honed over decades.

A battleship is usually armored to withstand an attack from guns the size of its own, but the armor scheme of the preceding North Carolina class was only proof against 14-inch (356 mm) shells (which they had originally been intended to carry), while the South Dakota and Iowa classes were designed only to resist their original complement of Mark V 2,240 lb (1,020 kg) shells, not the new "super-heavy" 2,700 lb (1,200 kg) APC (Armor Piercing, Capped) Mark7 VIII shells they actually used. The Montanas were the only US battleships designed to resist the Mark VIII.

Until the authorization of the Montana class all US battleships were built within the size limits for the Panama Canal. The main reason for this was logistical: the largest US shipyards were located on the East Coast of the United States, while the United States had territorial interests in both oceans. Requiring the battleships to fit within the Panama Canal took days off the transition time from the Atlantic Ocean to the Pacific Ocean by allowing ships to move through the canal instead of sailing around South America. By the time of the Two Ocean Navy bill, the Navy realized that ship designs could no longer be limited by the Panama Canal and thus approved the Montana class knowing that the ships would be unable to clear the locks. This shift in policy meant that the Montana class would have been the only World War II–era US battleships to be adequately armored against guns of the same power as their own.