 Up until the 1980s the Port of London Authority (PLA) dockmasters were responsible for five large enclosed dock systems and miles of quayside isolated from the tides by locks.These systems were London and St Katharine Docks, Surrey Commercial Docks, West India and Millwall Docks, Royal Docks, and Tilbury Docks.Of these only Tilbury is operational, along with DP World's London Gateway.