Operation Torch
Rosneath House became American staff headquarters and the planning centre for 'Torch' as thousands of U.S. navy, marine corps and army personnel arrived at the base to practise amphibious landing techniques at Rosneath and around the Clyde sea-lochs. The densely wooded Green Isle area near Rosneath House provided cover for living quarters capable of holding some 6,000 men. American troops were also billeted with local families in the Helensburgh area, along with British commandos with whom they trained for the African landings.
Following the success of Torch in late 1942, Rosneath Base was returned to the R.N. with the reservation of areas for use by the U.S.N. - the Clachan House 'seabee' camp, dock space for the submarine depot ship U.S.S. Beaver and the boats of Submarine Squadron 50 and the Portkil hospital complex.