Fort Bullen was constructed around 1827 on the north bank, opposite the Six-Gun Battery at State House, to cover the escape route for foreign ships entering and exiting the river. With gun batteries on both sides of the river mouth, the British finally had full control over all trade on the River Gambia.

During the Second World War Fort Bullen was again put to use as an observatory and artillery base by the British Army as a means to protect against a possible attack from the French Vichy Government which was controlling Senegal.