The Humber Forts are two large fortifications in the mouth of the Humber estuary in northern England: Haile Sand Fort (53°32′4″N 0°2′1″E / 53.53444°N 0.03361°E / 53.53444; 0.03361 (Haile Sand Fort)) and Bull Sand Fort (53°33′43″N 0°4′3″E / 53.56194°N 0.0675°E / 53.56194; 0.0675 (Bull Sand Fort)).
The two forts were planned in 1914 to protect the entrance to the estuary. They stand 18 metres (59 ft) above the water and have a diameter of 25 metres (82 ft). There was accommodation for 200 soldiers. Starting in May 1915, they took more than four years to build and construction was not finished until December 1919. During World War II they were reactivated and modernised. The forts were regularly attacked by enemy aircraft. During this time a netting was put up to prevent enemy submarines travelling up the estuary to Hull or Grimsby. The forts were finally deserted by the military in 1956.
Haile Sand Fort is the smaller of the two and is situated around the low water mark between Cleethorpes and Humberston on the Lincolnshire coast.
Bull Sand Fort is 1.5 miles (2.4 km) from shore off Spurn Head. It is a 4 storey concrete building with 12-inch (300 mm) of armour on the seaward side, and originally armed with four 6-inch guns, built with great difficulty as its sandbank is 11 feet (3.4 m) below low water. In 1987 it was given a Grade II Listed Building status. In 1997 it was sold to the Streetwise Charitable Trust who are restoring the fort for use as a drug rehabilitation facility. Administratively, it is within the East Riding of Yorkshire.