You may have heard of the SAS (Special Air Service) - the UK military’s renowned special forces unit whose actions gained global attention during the 1980 Iranian embassy siege.
The Royal Navy describes the Special Boat Service (SBS) as its "answer to the SAS".
The Navy's branch of the special forces is also highly skilled and secretive over the detail of its operations.
The SBS mainly recruits from the Royal Marine Commandos - a part of the military already considered to be an elite force.
It is an elite maritime counter-terrorism unit, made up of small teams who exploit the element of surprise to undertake daring undercover raids, the Navy says.
At the weekend, SBS personnel stormed an oil tanker off the Isle of Wight following a suspected hijacking.
Around 16 members of the SBS were involved in the operation, supported by airborne snipers, who secured the vessel in around nine minutes.
The SBS began life in the Second World War as a specialist unit trained to undertake difficult amphibious operations.
It was first referred to as the 'Folbot Troop', named after the wood and canvas kayaks used by the unit, before being redesignated as the 'Special Boat Section'.
In April 1943, breaking off from the SAS, it went under the command of Lord Jellicoe, as the ‘Special Boat Squadron’.
In the service’s infancy, men would paddle ashore on small vessels launched from submarines in order to sabotage enemy equipment and infrastructure.
In 1983, the unit was renamed the Special Boat Service.
The SBS still plays an active, although a very secretive, role in military operations.
The SBS and SAS have a long-standing rivalry, with both striving to be considered the world's most elite special forces unit.
Recruits for both must undergo some of the toughest selection processes on the planet and the UK Special Forces are thought to have an average 90% failure rate for selection.
Cover image: Royal Marines, from whom the SBS recruits most of its personnel, conducting fast-rope training (Picture: Royal Navy).