The Marine Policing Unit (MPU) is the waterborne policing unit of London's Metropolitan Police Service, forming part of the Met Taskforce (MO7) within Met Operations. Its 22 vessels are responsible for waterborne policing of the River Thames in Greater London and supporting the rest of the Metropolitan Police and to the City of London Police when dealing with incidents in or around any waterway in London. A specialist underwater and confined-spaces search team carries out searches throughout the Metropolitan Police District. The unit also has 24 officers who are trained in rope access techniques and trained to carry out searches and counter-demonstrator operations at height. In 1839 the Marine Police Force was merged into the Metropolitan Police as the Thames Division. It held that name until being renamed the Marine Support Unit in 2001 and taking on its present name seven years later. The unit is still headquartered at Wapping, where a former carpenters' workshop also houses the River Police Museum, founded in 1974 and now curated by John Joslin and Rob Jeffries, two former officers with the unit. Area of responsibility Originally focusing on the Pool of London, since the 19th century it has had responsibility for the 47 miles of the Thames between Hampton Court in the west and Dartford Creek in the east. This includes the stretch of river within the City of London, since the City of London Police does not have its own marine unit. Above Hampton Court, Surrey Police have responsibility for policing but a launch is supplied by the Environment Agency. Below Dartford Creek, responsibility lies with both Essex Police and Kent Police, who have combined forces and formed a joint marine unit, with Kent based at Sheerness and Essex based at Burnham-on-Crouch. Ranks Before 1839 the River Police held the ranks of 3rd, 2nd and 1st Inspector due to the special powers invested to Inspectors on the river by legislation regarding the boarding of vessels on the Thames. These ranks were retained when the River Police became Thames Division, uniquely among Metropolitan Police divisions and taking the place of Sergeants or Station Sergeants in the Metropolitan Police's other divisions. 3rd Class Inspectors were ranked and paid as Sergeants in the rest of force, 2nd Class Inspectors as Station Sergeants and 1st Class Inspectors as substantive Inspectors. These ranks were replaced by normal Metropolitan Police ranks in 1903, though for many years after