Three Janus-class torpedo-boat destroyers (TBDs) served with the Royal Navy.

Janus, Lightning and Porcupine were ordered under the 1893-94 Programme, all laid down on 28 March 1894 at Palmer's shipyard at Jarrow and launched during 1895.

They displaced 275 tons (light), were 204 feet 6 inches (62.33 m) long and produced 3,900 hp (2,900 kW) from their Reed water tube boilers which gave them a top speed of 27 knots (50 km/h; 31 mph).

Under the 1893–1894 Naval Estimates, the British Admiralty placed orders for 36 torpedo-boat destroyers, all to be capable of 27 knots (50 km/h; 31 mph), the "27-knotters", as a follow-on to the six prototype "26-knotters" ordered in the previous 1892–1893 Estimates.

As was typical for torpedo craft at the time, the Admiralty left detailed design to the builders, laying down only broad requirements.