Hildur-class monitor

The Hildur-class monitors consisted of seven monitors built for the Swedish Navy in the 1870s. They were sold in 1919 and most were converted into fuel oil barges. One such ship, HSWMS Sölve, has been converted into a museum ship.

Design and description
The Hildur-class monitors were designed by Lieutenant John Christian d'Ailly, from a proposal by John Ericsson, for the defense of Lake Mälaren and the Stockholm archipelago. The ships were 39.78 m long overall and had a beam of 8.72 m. They had a draft of 2.7 m and displaced 460 t. The crew of the first two monitors, Hildur and Gerda, numbered 42 officers and men, the others had 48-man crews. Hildur and Gerda only had a stern rudder, the other had rudders at bow and stern. Bow rudders were fitted to the older ships when they were reconstructed.

The Hildurs had a pair of two-cylinder horizontal-return connecting-rod steam engines, each driving a single propeller using steam from two cylindrical boilers. The engines produced a total of 133 ihp in the first two ships and 155 ihp in the later ones which gave the monitors a maximum speed of 8 kn. The ships carried 23 - 25 t of coal.

The monitors were equipped with one 240 mm M/69 rifled breech loader, mounted in a long, fixed, oval-shaped gun turret. The gun weighed 14670 kg and fired projectiles at a muzzle velocity of 397 m/s. At its maximum elevation of 7.5° it had a range of 3500 m. The gun and its turret in Folke were oriented to the rear. Hildur and Gerda were rearmed with a 120 mm quick-firing gun as well as three 57 mm quick-firing guns 1890; the other were similarly rearmed later in the 1890s or the early 1900s.

Most of the ships of the Hildur class had a complete waterline armor belt of wrought iron that was 76 mm thick with a 19 mm deck. Bjorn and Ulf had a 95 mm belt while Folke's belt ranged from 48 mm forward to 76 mm aft. The face of the gun turret was protected by 418 mm of armor, while its sides were 356 mm thick. The conning tower protruded from the top of the turret and was protected by 254 mm of armor.

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