HMS Unicorn was a 28-gun Lyme-class sixth-rate frigate of the Royal Navy. She was originally ordered as a 24-gun ship to the draft of the French privateer Tyger. The third vessel of the Royal Navy to bear the name, Unicorn, as well as HMS Lyme which was a near-sister, were the first true frigates built for the Royal Navy. They were actually completed with 28 guns including the four smaller weapons on the quarterdeck, but the latter were not included in the ship's official establishment until 22 September 1756. The two ships differed in detail, Unicorn having a beakhead bow, a unicorn figurehead , two-light quarter galleries and only five pairs of quarterdeck gunports, while Lyme had a round bow, a lion figurehead, three-light quarter galleries and six pairs of quarterdeck gunports.