In 1793, at the outbreak of war between Britain and revolutionary France, harbour batteries were hastily erected to secure Halifax from attack by sea. In the 19th century York Redoubt and the Citadel used signal flags to keep each other informed of ships' movements. During the First World War, the site was used as barracks for assigned infantry and for troops waiting to go overseas. Early in the Second World War, the Redoubt was the nerve centre for harbour defences, and included an anti-submarine net. York Redoubt remained in military use until 1956.