Monument MPM1931 - Chain Boom

A section of a chain boom used to defend the entrance to Portsmouth Harbour uncovered on the beach south of 18 Gun Battery on two separate occasions in 1972 and 1977.

A section of a chain boom used to defend the entrance to Portsmouth Harbour was uncovered on two separate occasions in 1972 and 1977. The section of chain appears to have consisted of six oblong links and a round link attached to a timber structure. The only information relating to the find is a museum information file containing correspondence. The chain was not excavated as part of an archaeological investigation and the correspondence does not state whether it was recovered, but it is not held in the museum collection. The location of the find has been estimated from plans and a description of the site in the information file. [1]


1972
Six links belonging to a chain boom were excavated on the beach south of 18 Gun Battery in November 1972. The correspondence describes the sections of chain as 5 links and a 'master link'. The following items were also recorded as having been found; 13 coins dating from between 1774 and 1948, 3 wooden posts approximately 11in x 7in, 4 timber beams and a wrought iron ring with a 27in diameter embedded in a 'block of crude cement and timber framing surround'. [1]


1977
The chain boom was uncovered by a family in November 1977. The description given from the finder in the correspondence file is that it consisted of 'six oblong 4ft links' connected to 'a round link which forms part of a large raft like structure buried in the beach….the raft is made of square section timbers held together by iron "pins" of about 1" diameter'. A photograph in the museum information folder shows the round link and first oblong link. [1]



The first documented chain boom was made in 1522 although it is possible this replaced an earlier one. Replacement chains are known to have been made in 1664 and 1779, as the metal was corroded by the sea. [2]

The chain boom operated between two towers situated on either side of the harbour entrance (see MPM442 Round Tower). In the event of an attack the chain would have been raised to prevent enemy vessels from entering the harbour. It was kept taught by capstans situated on either shore. The remains of the capstan on the Portsmouth side can be seen in Capstan Square on the north side of the Round Tower. [2]

Two sections of chain found prior to the 1970s (now joined together) are held in the Portsmouth Museum Service collection and are on display at Southsea Castle (ref: 1945/1 and 1963/109).

<1> Portsmouth Museum Service, ?, Uncovering Chain Defence Boom (Unpublished document). SPM534.

<2> Corney, A, 1973, Fortifications in Old Portsmouth - A Guide (Bibliographic reference). SPM388.