John McArthur (1755–1840) was a British naval officer, known also as an author. Early life McArthur entered the Royal Navy in 1778, as assistant clerk on board on the North American station. When Eagle came home McArthur was moved into the cutter , and on 22 March 1779 was promoted to be purser of her, for his gallantry in boarding a French privateer in an engagement of the American Revolutionary War off Le Havre on 14 March. In November Rattlesnake lent her small assistance to in capturing the Spanish frigate ; and, when the prize was commissioned for the Royal Navy, McArthur was promoted to be her purser. Work on signalling During the war McArthur was often on duty, observing signals. In 1790, on his own account, he proposed a new code of signals to the Admiralty, which caught the attention of Lord Hood, then First Sea Lord, and when in the Russian armament of 1791, he hoisted his flag in command, he made McArthur his secretary. He hoped to try out McArthur's signals; but there was an issue about introducing a new code to supersede that of Lord Howe, and McArthur is said to have recast his, remodelling it on the basis of Howe's. After approval by Howe, it was tested and used in the experimental cruise of 1792. While the new code was then adopted, Sir Home Popham's had generally taken over by the middle of the next decade. By 1799 McArthur was claiming to be the real author of the code known by the name of Lord Howe, but may have only seen it into print. Purser of Victory In 1793, when Hood went out as commander-in-chief in the Mediterranean, McArthur was again his secretary, being appointed also purser of . His duties at this time were complex: correspondence in three foreign languages, interpreter, and as Hood's representative in disbursements of public money, both to the British forces and to those of the allies. For some time there was no English commissary-general, and he had to act in that capacity. He was also prize agent for the fleet; his duties as purser of Victory were performed by a deputy. When Hood, after returning to England, was ordered to strike his flag, McArthur went back to the Mediterranean as simple purser of Victory. As soon as the ship joined the fleet, Rear-Admiral Robert Man hoisted his flag on