The 1650 Programme of six 510-ton Fourth Rate vessels was initiated by the Council of State on 16 November 1649. On 2 January 1650 the Admiralty Committee confirmed that six 'frigates' had been ordered at a cost of 6.10.0d per ton. The ships would be built under contract with the exception of one ship built in Dockyard. The ships were all named by 16 August 1650 and launched by the end of the year. Each ship was to carry initially 34 guns and 150 men, although this would increase over time
The construction of one vessel was assigned to Deptford Dockyard with the remainder contracted to private builders. The contract dimensional data was a keel length of and a breadth of , producing a builder's measurement tonnage of tons at a contract price of 6.10.0d per ton; the actual measurements as built are set out below. Soon after their first service, most were modified to have a forecastle added (to protect the upper deck, but not to carry guns) and were girdled (another layer of timbers added on each side), increasing their breadth (and consequently their BM tonnage) and enabling them to carry a heavier armament without jeopardising their stability. The ships were originally to have 34 guns and a manning level of 150, however, this was later increased to 40 guns with 180 men by December 1653, and for the surviving ships by 1666 to 46 guns with 170 men (in Foresight and Assistance) or to 48 guns with 180 men (in Reserve, Advice and Centurion). The guns were generally culverins on the lower deck (LD), demi-culverins on the upper deck and sakers on the quarterdeck (QD).