[3] The monitors were equipped with one 240-millimeter (9.4 in) M/69 rifled breech loader, mounted in a long, fixed, oval-shaped gun turret.

The gun weighed 14,670 kilograms (32,340 lb) and fired projectiles at a muzzle velocity of 397 m/s (1,300 ft/s).

[1] Most of the ships of the Hildur class had a complete waterline armor belt of wrought iron that was 76 millimeters (3 in) thick with a 19-millimeter (0.7 in) deck.

The conning tower protruded from the top of the turret and was protected by 254 millimeters (10 in) of armor.

[5] During Hildur's gunnery trials in 1872, her shells penetrated the walls of Vaxholm Fortress in three shots.