The Second Boer War started in October 1899 with a Boer offensive into the British-held Natal and Cape Colony areas. Congreve arrived in South Africa and was posted as a brigade major in the Ladysmith relief force. He was present at the Battle of Colenso when British troops commanded by Sir Redvers Buller attempted to cross the Tugela River to relieve the besieged city of Ladysmith. The Boers repelled all British attempts to cross the river, and was forced to retreat in one of their biggest defeats of the war.