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During World War II, the loch was used a submarine base. From 1961–1992, it was used as a US Polaris nuclear submarine base. In 1992, the Holy Loch base was deemed unnecessary following the demise of the Soviet Union and subsequently withdrawn.
Open to the Firth of Clyde at its eastern end, the loch is approximately one mile wide and between two and three miles (5 km) long, varying with the tide. The town of Dunoon on the Cowal peninsula lies on the shores of the Clyde just to the south of the loch, and houses continue round the villages of Kirn, Hunter's Quay at the point with the landing slip for Western Ferries, Ardnadam and past Lazaretto Point, the village of Sandbank, with open countryside at the end of the loch, then on the northern shore Kilmun, and at Strone Point the village of Strone continues round to the western shore of the Clyde, almost joining Blairmore on Loch Long. The name Holy Loch is believed to date from the 6th century, when Saint Munn landed there after leaving Ireland.
All the villages used to have piers served by Clyde steamers, and now Western Ferries runs between Hunters Quay and McInroy's Point on the outskirts of Gourock, while the Caledonian MacBrayne service runs from Dunoon to Gourock pierhead. At the end of the loch a road runs past the Benmore Botanic Garden and Arboretum (also known as the Younger Botanic Gardens) to scenic Loch Eck and on towards Oban.
Robertson's Yard 
Alexander Robertson started repairing boats in a small workshop at Sandbank in 1876, and Alexander Robertson and Sons Ltd (Yachtbuilders) went on to become one of the foremost wooden boat builders on the Clyde. Their 'golden years' were in the early 20th century when they started building classic 12 & 15 metre racing yachts. Robertsons was chosen to build the first 15-metre yacht designed by William Fife (Shimna, 1907). More than 55 boats were built by Robertsons in preparation for the First World War and the yard remained busy even during the Great Depression in the 1930s, as many wealthy businessmen developed a passion for yacht racing. During World War II the yard was devoted to Admiralty work, producing a wide range of large high speed Fairmile Marine Motor Boats (MTBs and MGBs).
After the war the yard built the successful one-class Loch Longs and two 12-metre challengers for the America's Cup: Sceptre (1958) (17 tonnes) and Sovereign (1964). The Robertson family sold the yard in 1965, and it was turned over to GRP production work (mainly Pipers and Etchells). During its 104-year history, Robertson's Yard built 500 boats, many of which are still sailing. The yard ceased trading in the early 1980s and the site was levelled soon after. The site has since been consumed by residential building and the new Holy Loch Marina development.
World War II 
During World War II the loch was used by the Royal Navy as a submarine base, served by the depot ship HMS Forth (1938). The loch was used extensively for trials and exercises by Royal Navy submarines during the war, the submarines HMS Vandal (P64) and HMS Untamed (P58) were lost in the Clyde after being sunk by accidents during exercises. Untamed was later salvaged.
Between 1961 and 1992, Holy Loch was the site of the United States Navy's FBM Refit Site One (FBM: Fleet Ballistic Missile). It was the home base of Submarine Squadron (SUBRON) 14, part of Submarine Force, U.S. Atlantic Fleet. To make maximum usage of its submarine-launched ballistic missile (SLBM) deterrent force, American military had determined that it required an overseas base for refit and crew turnover. Negotiations with the British Government began as early as March 1959 when President Dwight D. Eisenhower mentioned the need to British Prime Minister Harold Macmillan at a meeting at Camp David.
Holy Loch was one of several locations on or near the Firth of Clyde considered for the refit site. Others were Faslane, the channel between Largs and Cumbrae, Rosneath Bay, and Rothesay Bay. Site selection criteria included the requirements for a sheltered anchorage, relative proximity to an international airport, and sufficient shore facilities to provide housing for military personnel and their families. Agreement for the use of Holy Loch was reached near the end of 1960 and the arrival of the first tender, USS Proteus (AS-19) scheduled for December. Divisions within the British government and concerns about protests by the Campaign for Nuclear Disarmament (CND) caused her arrival to be rescheduled to 3 March 1961.
Between 1961 and 1982, the Naval Support Activity ashore was administered by US Naval Activities London. In 1982, Naval Support Activity (NAVSUPPACT), Forward Base, Holy Loch, Scotland became its own command. NAVSUPPACT ultimately managed 42 facilities and leased 342 housing units for Navy personnel and their dependents.
|March 1961||January 1963||USS Proteus (AS-19)||Commenced first site one refit 6 March 1961. (USS Patrick Henry (SSBN-599))|
|January 1963||August 1966||USS Hunley (AS-31)|
|August 1966||May 1970||USS Simon Lake (AS-33)|
|May 1970||November 1975||USS Canopus (AS-34)|
|November 1975||January 1982||USS Holland (AS-32)|
|January 1982||June 1987||USS Hunley (AS-31)|
|June 1987||March 1992||USS Simon Lake (AS-33)|
|June 1961||February 1992||USS Los Alamos (AFDB-7)||February 1964, completed the first "off center" docking of a Polaris submarine|
Laurel Clark, known to her shipmates as “Doc Salton”, was assigned as the Radiation Health Officer and Undersea Medical Officer at SUBRON 14. Clark was one of the astronauts who perished in the Space Shuttle Columbia disaster on 1 February 2003.
In 1992, the base was deemed unnecessary following the demise of the Soviet Union and withdrawn. The last submarine tender to be based there, the USS Simon Lake (AS-33), left Holy Loch in March 1992.
- Lavery, Brian (September 2001). "The British government and the American Polaris base in the Clyde". Journal for Maritime Research. Archived from the original on 2005-05-03.
- "Dunoon and the US Navy". Argyllonline.co.uk. Retrieved 2010-01-31.