The S90 class of torpedo boats was a group of large torpedo boats built for the German Imperial Navy (Kaiserliche Marine) in the early 20th century. They were Hochsee-Torpedoboot ("High seas torpedo boat") built to varying designs by Schichau at Elbing (36 vessels) and Germaniawerft at Kiel (12 vessels). German torpedo boats were designated by shipbuilder, with the first letter of their designation reflecting their builder.
These 48 vessels were built to ten different designs over the period 1898 to 1907. Thus they varied in dimensions, and they gradually increased in size as more vessels were built. The boats were long at the waterline and long overall. They had beam (nautical) of and a draft of . The hull for each boat was divided into eleven watertight compartments, though after , a twelfth compartment was added. They had a crew of two officers and fifty-five enlisted men, though some of the boats had larger crews; had four more sailors, while G132 had twelve more men, and had a crew of three officers and 78 enlisted. When serving as half-flotilla flagships, the boats would have a flotilla leader's staff of four officers and eleven enlisted men in addition to the standard crew. The vessels carried a yawl and a dinghy apiece.
The S90-class boats were propelled by a pair of vertical, 3-cylinder triple expansion steam engines that drove a pair of three-bladed screw propellers. Steam was provided by three coal-fired water-tube boilers. Two boats, and , were fitted with Parsons steam turbines instead of the older reciprocating engines; G137 also received an additional boiler. The reciprocating engine-powered boats were rated at from . Meanwhile, S125 and G137 were rated at and , and and , respectively. The boats had storage capacity for of coal. As a result, cruising radius varied significantly, from at . Each vessel was equipped with one or two 110-Volt generators for electrical power. Steering was controlled with a pair of rudders, one at the stern and the other in the bow.
Most of the ships of the class were armed with a main battery of three SK L/40 guns in single pivot mounts. They were supplied with a total of 252 shells that weighed . The guns had a muzzle velocity of and a maximum range of at their highest elevation of 20 degrees. G132, , , and were equipped with four SK L/55 guns in single gun mounts. These guns fired a similar 1.75 kg shell at a muzzle velocity of . The guns could elevate up to 20 degrees, at a maximum range of . was equipped with two of the 5.2 cm guns and one gun, while had three 5.2 cm guns and one 8.8 cm gun. The 8.8 cm gun fired a shell weighing at a muzzle velocity of . The gun could be elevated to 25 degrees, for a maximum range of . Many of the boats were rearmed throughout their time in service, trading their 5 cm or 5.2 cm guns for the more powerful 8.8 cm guns. All ships of the class carried three deck-mounted single torpedo tubes with five torpedoes.
Most of the ships served into World War I. S90 sank the on 17 October 1914, and was scuttled at Tsingtao later that day. Four of these boats took part in the Battle off Texel on the exact same day, in which a British light cruiser and four destroyers destroyed the Seventh Half-Flotilla consisting of S119, S115, S117 and S118.