HMS Alarm was a 32-gun fifth-rate Niger-class frigate of the Royal Navy, and was the first Royal Navy ship to bear this name. She was built at King's Yard in Harwich by John Barnard.

Copper-sheathed in 1761, she was the first ship in the Royal Navy to have a fully copper-sheathed hull.

Alarm initially saw deployment in the West Indies, where she experimentally had her hull sheathed in a thin layer of copper. Firstly it was intended to reduce the considerable damage caused by the teredo woodworm, and secondly the well-established toxic property of copper was expected to lessen the speed-killing barnacle growth which always occurred on ships' hulls. Alarm's hull was first covered with soft stuff, which was hair, yarn and brown paper, and then covered with a layer of copper plates.

After a two-year deployment to the West Indies, Alarm was beached in order to examine the effects of the experiment. The copper had performed very well in protecting the hull from invasion by worm, and in preventing the growth of weed, for when in contact with water, the copper produced a poisonous film, composed mainly of oxychloride, that deterred these marine creatures. Furthermore, as this film was slightly soluble it gradually washed away, leaving no way in which marine life could attach itself to the ship. Satisfied that the copper had had the desired effect, the Admiralty introduced copper sheathing on a number of frigates.

In 1776 Alarm was resurveyed. It was soon discovered that the sheathing had become detached from the hull in many places because the iron nails which had been used to fasten the copper to the timbers had been "much rotted". Closer inspection revealed that some nails, which were less corroded, were insulated from the copper by brown paper which was trapped under the nail head. The copper had been delivered to the dockyard wrapped in the paper which was not removed before the sheets were nailed to the hull. The obvious conclusion therefore, and the one which had been highlighted in a separate report to the Admiralty as early as 1763, was that iron should not be allowed direct contact with copper in a sea water environment if severe corrosion of the iron was to be avoided. Later ships were designed with this in mind. The Admiralty had largely suspended the programme of fitting ships with copper sheathing after the 1763 report, and had not shown any further interest in developing effective copper sheathing until 1775. In the meantime the copper sheathing was removed from Alarm, and several other test vessels until an effective solution to the corrosion problem could be developed.

Later in her career she was commanded by a young John Jervis, from 1769 onwards. He sailed for the Mediterranean in May and arrived in Genoa on 7 September. Aboard Alarm at this time was Samuel Hood, son of Alexander Hood, and one of the many members of the Hood family to serve at sea. Samuel Hood served aboard Alarm from November 1765 to July 1772, in the post of purser.

On the return voyage to England, on 6 April 1770, she was saved by Georges René Le Peley de Pléville from being wrecked off Marseille. Alarm had been battered by a storm in the evening and ran aground on the coast of Provence amongst boulders, and was in imminent danger of breaking up. Pléville quickly mustered the harbour pilots and rushed to the relief of the British. By the time he was able to board her, Alarm had already almost heeled over many times, and began to run aground. Pléville ordered a manœuvre that got her afloat again and brought her into harbour at Marseille. In gratitude for Pléville's actions, the Admiralty sent Jervis and Alarm back to Marseille in December to deliver a letter which read

Sir, the quality of the service which you have rendered to the frigate Alarm gives rise to the noble envy and admiration of the English. Your courage, your prudence, your intelligence, your talents have merited a crown on your efforts from Providence. Success has been your reward, but we pray you to accept as a homage rendered to your merit and as a pledge of our esteem and recognition, that which captain Jervis is charged with rendering back to you. In the name and order of my lords, Stephans