The Special Boat Service was originally known as the Extraordinary Boat Segment during WWII. It was later renamed the Exceptional Boat Unit before settling on its current name, the Special Boat Service. The SBS performs land and maritime operations, including counter-terrorism. It is comprised of a single squadron from the Royal Marines based in Poole. The SBS operates in units assigned to specific tasks, such as the C and X units for general duties, the S unit for operations involving small submarines and boats, and the M unit for counter-terrorism operations.