Nix-class aviso

During the initial stage of the First Schleswig War in 1848, it had become clear to Prince Adalbert of Prussia that the small Prussian Navy was powerless against the significantly larger Danish Navy, which led him to press for increased naval spending.^[1] The Danish blockade had forced the Prussian government to requisition packet steamers like Preussischer Adler to defend German merchant traffic. With the demobilization following a truce in August 1848, the navy relinquished the civilian vessels, but Adalbert continued to push for a strengthened fleet.^[2]

Adalbert initially conceived of flat-bottomed steam gun boats that could operate in shallow coastal waters. He submitted design requests to the German shipyards Klawitter and Devrient and the British firm Robinson & Russell; the latter had more experience than the German builders, so Adalbert awarded the contract to Robinson & Russell. Adalbert and the British naval architect John Scott Russell agreed on building a pair of small avisos with iron hulls. The hull lines should allow the vessels to steam either ahead or astern, with a rudder at either end to control steering in both directions.^[1] Design work on the paddle steamers was completed in 1849,^[3] and they were authorized in 1850; payment was made in March and King Friedrich Wilhelm IV approved the names Nix and Salamander, which had been suggested by Adalbert. The contract signed with Robinson & Russell also included British assistance with the construction of the larger paddle steamer Danzig in Prussia.^[1][4]

The Nix class ships were 53.05 m (174 ft 1 in) long at the waterline and 53.85 m (176 ft 8 in) long overall, with a beam of 7.2 m (23 ft 7 in) over the hull and 12.4 m (40 ft 8 in) over the paddle wheels. With a design displacement of 389 t (383 long tons) and a full-load displacement of 430 t (420 long tons), they had a draft of 2 m (6 ft 7 in). The very shallow draft was designed to allow the vessels to cruise in the shallow waters along Prussia's coast. Their iron hulls incorporated transverse iron frames and wooden decks. The hulls were divided into thirteen watertight compartments and had a double bottom that ran for their entire length.^[1][3]

The ships were propelled by a pair of 2-cylinder single-expansion marine steam engines that turned a pair of paddle wheels, one on either side of the hull amidships. The paddle wheels each had fourteen paddles and they were 5 m (16 ft) in diameter. Steam for the engines was provided by four boilers, which were ducted into two funnels. The boilers were divided into two boiler rooms, one forward of the engine room and the other aft. Their propulsion system was rated at 600 metric horsepower (592 ihp) for a top speed of 13 knots (24 km/h; 15 mph). At a speed of 10 knots (19 km/h; 12 mph), they could steam for 2,500 nautical miles (4,600 km; 2,900 mi). To supplement the steam engines, the ships carried a sailing rig that consisted of two masts, each fitted with a square topsail and a lower lug sail, along with a forward staysail. The total sail area was about 350 m² (3,800 sq ft).^[3] As a measure of protection for the propulsion machinery, the coal bunkers were arranged abreast of the engine and boiler rooms, and it was thought that the iron hull would also increase the vessels' resistance to damage.^[1]

Their crew consisted of approximately four officers and seventy enlisted men. The ships carried four small boats of unrecorded type. Steering was controlled by a pair of rudders, one at the stern and one in the bow; both could be fixed. Nix and Salamander were good sea boats, but they had a wide turning radius and could not be steered at all while under sail. They carried an armament of four 25-pound mortars. The design initially called for four short-barrelled 12-pounder guns in addition to the mortars, but these were never installed.^[3]