Swift was the third of three small, fast vessels designed by Surveyor of the Navy Jacob Acworth to guard merchant shipping between North America and Britain after the declaration of war against Spain in 1739.

[1][a] She was ordered in December 1740 to be constructed by civilian shipwright Robert Carter on the waterfront at Limehouse, then fitted out, armed and commissioned at Deptford Dockyard.

Twelve lightweight half-pounder swivel guns (anti-personnel weapons) were mounted on posts along the sides of the deck, and two more four-pounder cannons were added by Admiralty Order in 1744.

She came within sight of the Spanish fleet in St Simons harbour on 13 July, accompanied by her sister ship Hawk and the ageing 24-gun post-ship Flamborough.

In February 1745 Denis was transferred to the captaincy of the 26-gun sixth-rate HMS Greyhound, and Swift was reassigned to Commander John Hill under her previous orders for North Sea escort and patrol.