Admiral of the Fleet Sir Philip Louis Vian, GCB, KBE, DSO & Two Bars (15 June 1894 – 27 May 1968) was a Royal Navy officer who served in both World Wars.

Vian specialised in naval gunnery from the end of the First World War and received several appointments as gunnery officer. In the early 1930s, he was given command of a destroyer, HMS Active, and, later, various destroyer flotillas. During this phase of his career, in early 1940, he commanded a force that forcibly released captured British merchant sailors from the German supply ship Altmark in Jøssingfjord in then-neutral Norway and, later, his flotilla took an active role in the final action of the German battleship Bismarck.

Much of Vian's Second World War service was in the Mediterranean, where he commanded a cruiser squadron, defended several critical convoys and led naval support at the Allied invasions of Sicily and Italy. His wartime service was completed in command of the air component of the British Pacific Fleet, with successful actions against the Japanese in Sumatra and the western Pacific. Post-war, Vian served in the United Kingdom, as a Fifth Sea Lord and as Commander-in-Chief, Home Fleet. He retired in 1952 with the rank of Admiral of the Fleet, took up commercial directorships, and died at home in 1968.

Born the son of Alsager Richard Vian and Ada Frances Vian (née Renault), Vian joined the Royal Navy as an officer cadet in May 1907 and was educated at the Royal Naval Colleges at Osborne and Dartmouth. On passing out from Dartmouth in 1911, Vian and his term sailed for the West Indies on the training cruiser HMS Cornwall but the cruise was ended by grounding on an uncharted reef off Nova Scotia. He became a midshipman on the pre-dreadnought battleship HMS Lord Nelson, which was serving with the Home Fleet, on 15 January 1912.

At the start of the First World War, Vian remained on Lord Nelson which, as an obsolescent ship, was kept at Portland away from danger. This was disappointing for Vian, but when the ship was to be transferred to the Mediterranean he was posted to what he considered to be an even less desirable appointment. From October 1914 to September 1915, Vian served in HMS Argonaut, an old first-class protected cruiser patrolling in East African waters, on the lookout for the German cruiser Karlsruhe. He was confirmed as a sub-lieutenant in January 1915. Dissatisfied by the lack of action in Argonaut, Vian used a promise of help from William Fisher and subsequently received an appointment to HMS Morning Star, a modern Yarrow-built M-class destroyer, in October 1915. Whilst on this ship, he was a spectator at the Battle of Jutland, in which his ship played no active part. Promotion to lieutenant in 1917 (with seniority backdated to February 1916) resulted in two appointments as First Lieutenant in the destroyers HMS Ossory (September 1916) and HMS Sorceress (December 1917).

Following gunnery courses in 1916, 1918 and 1919 at the gunnery school (HMS Excellent), Vian obtained a First Class certificate in Gunnery in October 1919. Despite being slated for service with the British Military Mission in Southern Russia, he was loaned to the Royal Australian Navy for two years from January 1920 and served as Gunnery Officer of HMAS Australia, then the Australian flagship. On his return to the Royal Navy, Vian was given a series of appointments as gunnery officer, first, in January 1923, to the battleship HMS Thunderer, then serving as a cadet training ship. During this appointment, he was promoted to lieutenant commander on 15 February 1924. This was followed in 1924 by two appointments to C-class cruisers (HMS Champion and HMS Castor). There was a short period at the Devonport gunnery school (HMS Vivid) and another sea posting, to the battleship HMS Emperor of India in the Mediterranean Fleet in May 1925.

There followed two foreign postings, still as a gunnery specialist. First in February 1927 to HMS Royal Sovereign, in the Mediterranean Fleet. This was followed, in November 1927, to HMS Kent, the then-flagship of the China Station, where he was promoted to commander on 30 June 1929. For the two years up to January 1933, Vian had a "shore" appointment at the Admiralty in London, with the Director for Staff Training and Development (DTSD), analysing practice gunnery statistics. He then attended a short Tactical Course in Portsmouth and subsequently took command (his first), in March 1933, of the destroyer HMS Active and a Division within the 3rd Destroyer Flotilla (part of the Mediterranean Fleet).

A biography of the playwright Noël Coward refers to Coward meeting Vian at that time. Coward arrived at Bermuda on SS Roma on 28 May 1933 and boarded the light cruiser HMS Dragon on 30 May 1933. Vian's first words to Coward were "What the hell are you doing on board this ship?" However, after speaking to Coward and having gin with him in the captain's cabin, Vian permitted Coward to stay on the ship for a cruise on the ship ending on the Pacific side of the Panama Canal, Coward finally ending up in Trinidad some time later.