James Joseph Magennis, VC (27 October 1919 – 12 February 1986) was a Belfast-born sailor and recipient of the Victoria Cross, the highest award for gallantry in the face of the enemy that can be awarded to British and Commonwealth forces. He was the only native of Northern Ireland to receive the Victoria Cross in the Second World War.

Magennis was part of several operations involving X-Craft midget submarines in attacks on Axis ships. In July 1945, Magennis was serving on HMS XE3 during Operation Struggle. During an attack on the Japanese cruiser Takao in Singapore, Magennis showed extraordinary valour and bravery by leaving the submarine for a second time in order to free some explosive charges that had got caught. His commanding officer, Lieutenant Ian Edward Fraser, was also awarded the Victoria Cross for his actions during the operation.

James Magennis was born on 27 October 1919, at Majorca Street, West Belfast, Ireland. He was from a working class Roman Catholic family and attended St Finian's Primary School on the Falls Road, Belfast. On 3 June 1935 he enlisted in the Royal Navy as a boy seaman (spelling his surname Magennis).

Magennis served on several warships between 1935 and 1942, when he joined the submarine branch. Before joining the submarine branch, Magennis served on the destroyer Kandahar, which was mined off Tripoli, Libya, in December 1941, while Magennis was on board. The ship was irreparably damaged and was scuttled the following day.

In December 1942, Magennis was drafted into the Royal Navy Submarine Service and, in March 1943, he volunteered for "special and Hazardous duties" – which meant midget submarines, or X-craft. He trained as a diver, and in September 1943, took part in the first major use of the X-craft during Operation Source. Two submarines, HMS X7 and HMS X6, penetrated Kåfjord, Norway, and disabled the German battleship Tirpitz. For his part in the attack Magennis was Mentioned in Despatches "[f]or bravery and devotion to duty" in 1943.

In July 1945, Magennis, as acting leading seaman, was serving as the diver on the midget submarine HMS XE3, under the command of Lieutenant Ian Edward Fraser, as part of Operation Struggle. They were tasked with sinking the 10,000 ton Takao, the first of the Takao-class cruiser. She was berthed in the Straits of Johor, Singapore, acting as an anti-aircraft battery. On 30 July, XE3 was towed to the area by the submarine Stygian. She slipped her tow at 23:00 for the 40-mile (64 km) journey through hazardous wrecks, minefields and listening posts to reach the Takao. After arriving at the Takao at 13:00 on 31 July, Magennis slipped out of the wet-and-dry chamber and attached limpet mines to the Takao under particularly difficult circumstances. He had to chip away at barnacles on the bottom of the cruiser for 30 minutes, before being able to attach the limpets.

During this time, Magennis' breathing apparatus was leaking and he returned to the submarine after completion of his task very exhausted. On withdrawing, Fraser found that one of the limpet carriers which was being jettisoned would not release itself. Magennis immediately volunteered to free it, commenting: "I'll be all right as soon as I've got my wind, Sir." This he did, after seven minutes of nerve-racking work with a heavy spanner. On completion, Magennis returned to XE3 for the second time, allowing the four-man midget submarine to make its escape out to open sea to meet the waiting Stygian. Fraser was also awarded the Victoria Cross for his part in the attack; whilst Lieutenant William J. L. Smith, who was at the controls of XE3 during the attack, received the Distinguished Service Order. Engineer third class Charles Alfred Reed, who was at the wheel, received the Conspicuous Gallantry Medal.

HMS XE1 was supposed to be attacking another Japanese vessel as part of the same operation, but actually ended up also placing its explosives under the same target. XE1's commanding officer, Lieutenant John Elliott Smart, and Sub-Lieutenant Harold Edwin Harper, received the Distinguished Service Cross. Engineer fourth class Henry James Fishleigh and leading seaman Walter Henry Arthur Pomeroy received the Distinguished Service Medal. Engineer fourth class Albert Nairn, leading stoker Jack Gordan Robinson, and Able Seaman Ernest Raymond Dee were mentioned in dispatches for their part in bringing the two midget submarines from harbour to the point where the crews that took part in the attack took over.