The Alecto-class steam vessels (SV3) later reclassed as Third Class Sloops, were designed by Sir William Symonds, the Surveyor of the Navy.

A fifth unit was ordered (Rattler), but was reordered as a screw propelled vessel.

Alecto was the second named vessel since it was used for a 12-gun fireship, launched by King of Dover on 26 May 1781 and sold in 1802.

[2] Ardent was the fifth named vessel since it was used for a 64-gun third rate, launched at Blaydes of Hull on 13 August 1764, captured by the French off Plymouth on 17 August 1779, recaptured in April 1782 and renamed Tiger then sold in June 1794.

[3] Prometheus was the second named vessel since it was used for an 18-gun fireship, Launched by Thompson of Southampton on 27 March 1807, assigned to harbour service in May 1819, then renamed Veteran on 2 May 1839 and broken in August 1852.