admiralty arch - Admiralty Arch; admiralty arch - Triumphal arch in London. It is at the entrance from Trafalgar Square into St. James's Park, and commands a fine view along the Mall with the Victoria Memorial and Buckingham Palace at the other end. Designed by Sir Aston Webb, it is part of the national memorial to Queen Victoria. It is a triple arch connected by a bridge with the Admiralty offices, hence its name. The Admiralty library is housed in rooms surmounting the arch.