Born in Ceylon, to James Forbes and Caroline Forbes. His father was a tea-broker, founder of the merchant brokerage house Forbes and Walker Ltd. Charles Forbes was educated at Dollar Academy and Eastman's Royal Naval Academy. He joined the training ship HMS Britannia as a cadet on 15 July 1894. He was promoted to midshipman on 15 July 1896 and posted to the battleship in the Channel Fleet in September 1896 and to the armoured cruiser on the Pacific Station in January 1898. Promoted to acting sub-lieutenant on 15 January 1900, he returned to the United Kingdom for his promotion courses. Promoted to lieutenant on 15 January 1901, he was appointed to the battleship in the Mediterranean Fleet. In early April 1902 Forbes transferred to the armoured cruiser, also serving in the Mediterranean Fleet. After attending the gunnery school in 1903, he was assigned to Directing Staff at the gunnery school HMS Cambridge in June 1904. He then became gunnery officer in the armoured cruiser in the Mediterranean Fleet in May 1905 and gunnery officer in the battleship in the Channel Fleet in May 1908. After joining the staff of the Inspectorate of Target Practice in October 1910, he became gunnery officer in the battleship in the Home Fleet in February 1911 and then, having been promoted to commander on 31 December 1912, he returned to the gunnery school HMS Excellent in early 1913.
First World War
Forbes served in the First World War as Executive Officer in the battleship in the Mediterranean Fleet from November 1914 and saw action in the Dardanelles Campaign in April 1915. He became Flag Commander to Admiral Sir John Jellicoe, Commander-in-Chief of the Grand Fleet, in the battleship in October 1915 and saw action at the Battle of Jutland in May 1916 for which he was awarded the Distinguished Service Order on 15 September 1916. He moved on to become Flag Commander to Admiral Sir Charles Madden, Second-in-Command of the Grand Fleet, in the battleship in February 1917. He was awarded the Order of Saint Stanislaus, 2nd Class with Swords for his action during the Battle of Jutland on 5 June 1917. Promoted to captain on 30 June 1917, he was given command of the cruiser in the Grand Fleet in July 1917 and was present at the surrender of the German fleet in November 1918.
Forbes served in the Second World War as Commander-in-Chief Home Fleet, in which role he transferred his flag to the battleship in December 1939. His fleet suffered heavy losses including the aircraft carrier and nine destroyers during the Norwegian Campaign in Spring 1940. He was on board HMS Rodney when she came under air attack and was hit by a 500 kg bomb that pierced the armoured deck on 9 April 1940. Promoted to Admiral of the Fleet on 8 May 1940 and advanced to Knight Grand Cross of the Order of the Bath on 11 July 1940, he became Commander-in-Chief, Plymouth in May 1941. In that capacity he organised the defence of Plymouth from air attack, prosecuted attacks on enemy shipping using the harbour at Brest as well as other ports along the French coast, and also initiated the St Nazaire Raid in March 1942.
In 1909 Forbes married Agnes Millicent Ewen; they had a son and a daughter. Following the death of his first wife, he married Marie Louise Berndtson in 1921; they had one daughter. His younger brother was ColonelOswald Boyd Forbes.