Dreadnoughts mounted a uniform main battery of heavy-caliber guns; the number, size, and arrangement differed between designs. Dreadnought herself mounted ten 12-inch (305 mm) guns. 12-inch guns had been standard for most navies in the pre-dreadnought era and this continued in the first generation of dreadnought battleships. The Imperial German Navy was an exception, continuing to use 280-millimetre (11.0 in) guns in its first class of dreadnoughts, the Nassau-class.
Dreadnoughts also carried lighter weapons. Many early dreadnoughts carried a secondary armament of very light guns designed to fend off enemy torpedo boats. However, the caliber and weight of secondary armament tended to increase, as the range of torpedoes and the staying power of the destroyers expected to carry them also increased. From the end of World War I onwards, battleships had also to be equipped with anti-aircraft armament, typically a large number of light guns.
Dreadnoughts also very frequently carried torpedo tubes themselves. In theory, a line of battleships so equipped could unleash a devastating volley of torpedoes on an enemy line steaming a parallel course. In practice, torpedoes fired from battleships scored very few hits, while there was a risk that a stored torpedo would cause a dangerous explosion if hit by enemy fire.