Wikipedia
The Maplin Sands are mudflats on the northern bank of the Thames estuary, off Foulness Island, near Southend-on-Sea in Essex, England. They are valuable as a wildlife reserve, with a large colony of dwarf eelgrass (Zostera noltei) and associated animal communities.
A screw-pile lighthouse was built on the sands in 1838, which was possibly the world's first.
A plan to build a third airport for London on the sands was considered. The project would have included not just a major airport, but a deep-water harbour suitable for the container ships then coming into use, a high-speed rail link to London, and a new town for the accommodation of the thousands of workers who would be required. An attractive aspect of the plan was said to be that aircraft taking off against the prevailing wind would do so over the Thames Estuary, thus minimising noise nuisance on the ground. In 1973 a Special Development Order was made under the Town and Country Planning Acts granting planning permission for the project, and the Maplin Development Authority was constituted and began its work. The following year, however, the project became one of the many casualties of the 1973/74 oil crisis precipitated by the Yom Kippur War, and was abandoned in favour of a cheaper plan to enlarge Stansted Airport; the requirement for a container ship harbour was to be discharged by the development of Felixstowe.
The Maplin Sands were at that time, and remain, a military testing ground belonging to the Ministry of Defence - see Pig's Bay.