Vice-Admiral Sir Hugh Stirling Mackenzie, (3 July 1913 – 8 October 1996) was a Royal Navy officer who became Flag Officer Submarines and Chief Polaris Executive.

Educated at the Royal Naval College, Dartmouth, Mackenzie served in submarines during the Second World War becoming commanding officer of the submarine in March 1941, of in April 1941, of in which he sank of enemy shipping, and of , in which he conducted a single patrol of nearly .

Mackenzie went on to be commanding officer of the Underwater Detection Establishment at Portland in 1952, commander of the 1st Destroyer Squadron in June 1954 and Chief of Staff to the Flag Officer Submarines in December 1956. After that he became Captain of the Boys' Training Establishment in January 1959, Flag Officer Submarines in September 1961, and Chief Polaris Executive in spring 1963 before retiring in September 1968.

Early life Hugh Stirling Mackenzie was born in Inverness, Scotland, on 3 July 1913, the son of Dr Theodore Charles Mackenzie, the medical superintendent of the Inverness District Asylum, and his wife, Margaret (Madge) Wilson. His home, and birthplace, was Ruigh-Ard, the superintendent's residence. He had two older brothers, Charles and Alec, and a younger sister, Margaret.

At the age of nine, he was sent to Cargilfield Preparatory School, where his brother Charles was head boy, followed by his brother Alec the next year. In 1924, he appeared before the interview board and was given a medical examination as the first steps to admission to the Royal Naval College, Dartmouth. He was initially rejected on the grounds of deficient eyesight, but his father lodged an appeal, and had his sight examined by an eye specialist in Edinburgh, who declared that it met the Navy's standards. Another test at Queen Anne's Mansions in London cleared the way for him to sit the entrance examinations, which he passed.

Early naval career Mackenzie entered the Royal Naval College in January 1927, one of 51 members of the Anson Term, three of whom would not graduate in July 1930. They then received leave that lasted until September, which Mackenzie spent at home with his parents and three siblings at Ruigh-Ard. Due to cutbacks, there was no Cadet Training Cruiser for the class, and they were posted to the fleet for additional training. Mackenzie was posted to the battleship , part of the Mediterranean Fleet's 1st Battle Squadron. He embarked for the Mediterranean on the P&O ocean liner , on which the new fleet commander, Admiral Sir William Wordsworth Fisher, was also travelling, completing the voyage on the battleship . In addition to service on Ramillies, Mackenzie, who was promoted from officer cadet to midshipman on 1 May 1931, spent a fortnight on the aircraft carrier and three months on the destroyers and in the summer of 1932 in order to gain familiarity with the work of various ships of the fleet.

At the conclusion of his tour of duty in the Mediterranean in July 1933, Mackenzie passed his sub lieutenant's examination, and returned to England on the destroyer to rejoin the Anson Term for the six-month sub lieutenant's course at the Royal Naval College, Greenwich. After coursework that was interrupted by an operation on his left inner ear at the Royal Naval Hospital, Chatham, the midshipmen moved on to specialist courses in gunnery, torpedo, navigation and signals at , , and . He was promoted to sub lieutenant, with seniority backdated to 16 March 1934. Not liking the life on battleships, he applied for submarine duty. He was accepted, and sent to in January 1935, where he was trained as a submariner.

Mackenzie was posted to , one of the boats of the 4th Submarine Flotilla, which was based in Hong Kong as part of the China Station. During the summer, the flotilla moved north to Weihaiwei to escape the heat and humidity. He was promoted to lieutenant, with seniority backdated to 16 October 1935, and returned to England via Japan and the Trans-Canada Railway in August 1937. He joined the 2nd Submarine Flotilla, which was part of the Home Fleet, and based at Devonport. He was given command of HMS Mist, an old coal burner that was manned by spare crewmen assigned to the flotilla and commanded by the spare lieutenant. Soon after, the Mist was ordered to join the reserve fleet, into which she was reluctantly accepted. In May 1938, Mackenzie was assigned to . There was a serious incident when Seahorse was accidentally rammed by the destroyer . The submarine dived to avoid the destroyer, which did not detect it on asdic, but suffered damage to its periscopes. Both ships took several weeks to repair.

Second World War Osiris

In April 1939, Mackenzie was posted to . The boat was almost lost during a test dive when a rivet popped out. On 27 September 1939, Osiris sailed for Malta to join the 1st Submarine Flotilla. She embarked on her first war patrol on 31 May 1940, and was at sea when Italy declared war on the UK on 10 June 1940. On the night of 16 August, Osiris was on her third war patrol, attempting to interdict shipping between Italy and Albania, when she sighted a cargo ship off the Albanian coast. The ship, the Morea, was empty and riding high in the water. Two torpedoes were fired at range, but apparently passed beneath her. Osiris then closed to within and fired two more torpedoes, which also missed. She then surfaced and engaged Morea with her deck gun. Despite the brilliant flashes and considerable noise from the deck gun, there was no sign of activity on board, and shells were pumped into Morea until she started to sink.

Osiris departed Malta for her next war patrol on 9 September 1940, returning to the same vicinity. She found the area rich with targets moving troops and supplies from Italy to Albania for what would soon be revealed to be the Italian invasion of Greece. Osiris attempted to engage them, but for one reason or another, a whole series of attacks failed. On 13 September, she fired two salvoes of two torpedoes each at a range of at a convoy of three ships escorted by destroyers; all missed. But on 22 September she fired a full six-torpedo spread at a convoy at range. At first the crew thought that the torpedoes had again missed; but then there was an explosion, and the Italian torpedo boat Palestro was sunk. On returning to Alexandria, a launch brought the Osiris a Jolly Roger, which she flew to indicate a success.

It was Mackenzie's last patrol in Osiris. He received orders to return to England for the "Perisher", the five-week submarine Commanding Officers Qualifying Course. Because the Mediterranean was closed due to the war, he had to sail round the Cape of Good Hope in the . He was formally declared to have qualified for command of a submarine in February 1941, and assigned to the 7th Submarine Flotilla as a spare commanding officer. On 7 March 1941, he was given temporary command of an old boat used for training, . Heading down Lough Foyle in the early morning darkness on 10 March showing navigation lights, she encountered the heading in the opposite direction on the port (incorrect) side. As Lairdsbank approached the submarine, but without sighting it, she suddenly veered to starboard. Mackenzie ordered "full astern", but the two collided. Fortunately, although the bow of H28 was crumpled, the boat remained watertight, and Mackenzie was able to return to Derry for repairs. Lairdsbank suffered no damage and was unaware that there had been a collision. Admiral Max Horton told Mackenzie not to do it again. On 14 April, Mackenzie assumed command of another training boat, .

Thrasher In June 1941, Mackenzie received orders to rejoin the Mediterranean Fleet. This time he travelled to Alexandria through the Mediterranean as a passenger on the submarine . On 12 October, he assumed command of the submarine . A few days later he set out on his first war patrol in her (but Thrashers fifth), sinking an Italian schooner with the deck gun, and unsuccessfully engaged an Italian minesweeper. On the next patrol, Mackenzie attacked a three-ship convoy on 25 November, sinking the Italian cargo ship Attilio Deffenu with a torpedo. Thrasher had orders to insert a party of Yugoslav agents under the command of Stanislav Rapotec, but the mission was cancelled and Thrasher returned them to Alexandria. Thrasher set out again in January 1942, and found a large ship with an escort. Failing to gain a firing position, Mackenzie surfaced, overtook them, and attacked, sinking the Italian cargo ship Fedora.

Thrasher set out on her eighth war patrol on 13 February 1942. Off Suda Bay, Crete, Mackenzie found the German merchant ship Arkadia. It had five escorts, which Mackenzie took to be an indication that it was important. He fired a salvo of four torpedoes, and believed that he had hit something, but all missed. Thrasher was engaged by aircraft and surface ships, which dropped 33 depth charges. After Thrasher surfaced that night, two unexploded bombs were discovered. The first was disposed of by being dragged forward and lowered over the bow. The second presented more difficulty. On reading the patrol report, Admiral Andrew Cunningham ordered Mackenzie to write up the incident for gallantry awards to Roberts and Gould. They were awarded the Victoria Cross.

On 9 April, Mackenzie attacked a convoy. He fired a salvo of three torpedoes at the Italian merchant ship Gala. Although he observed a hit, he saw no evidence that it had sunk. It had. He attacked another small convoy on 13 April, sinking the German army cargo ship Atlas, which was struck by two torpedoes from a three torpedo salvo. Escort vessels dropped 19 depth charges on Thrasher. When she came up to periscope depth, Mackenzie saw one escort and a lighter. The escort left to rejoin the convoy, and Mackenzie surfaced in broad daylight and sank the lighter, the Italian Pilo 210 with his deck gun. On her tenth patrol, Mackenzie attacked the Italian armed merchant cruiser Brioni on 16 May, but she spotted the torpedoes and evaded them. Three days later he attacked and sank the Italian merchant ship Penelope. On her eleventh war patrol, Mackenzie sighted two cargo ships escorted by the , and sank the Italian merchant Sant Antonio. Six days later he sighted the Italian sloop Diana, Mussolini's yacht, and sank it. On 4 July, a German U-boat, , was sighted, but it evaded both Thrashers torpedoes and her gunfire. Thrasher was attacked by a Fleet Air Arm Fairey Swordfish of No. 815 Squadron on 26 July, causing considerable damage.

After repairs were effected, Thrasher set out again in September. Responding to a report from a shadowing Vickers Wellington bomber of an enemy ship escorted by two destroyers, Thrasher raced to intercept them on 4 September. This was the Italian merchant ship Padenna, escorted by the and . Mackenzie lined up an attack, but was thwarted at the last minute by the escorts. He then fired a salvo of three torpedoes from the stern torpedo tubes. Two hit, and the Wellington pilot reported that the ship blew up. On the next patrol Mackenzie sank a couple of schooners with gunfire on 12 October, the Italian tugboat Roma on 19 October, and the Italian merchant ship Lero on 20 October. Thrasher made an abortive attack on two merchant ships on 25 October, and was subjected to a severe depth charging by the two escorts, but managed to get away.

This was Mackenzie's last war patrol in Thrasher, which now returned to the UK. He was credited with sinking of enemy shipping. He was made a Companion of the Distinguished Service Order on 30 June 1942, and was promoted to lieutenant commander on 23 October, with seniority of 16 October. He was awarded a bar to his Distinguished Service Order on 19 January 1943. He was sent on a publicity tour to increase public awareness of the role that submarines were playing in the conflict, and appeared in a war movie, We Dive at Dawn.

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