You’ve probably heard of the SAS, the British military’s most renowned special forces unit who rose to fame in May 1980 as a result of their heroic involvement in the Iranian embassy siege.
But what do you know about the SBS? The Navy's branch of the special forces is equally as skilled and equally as secretive about their operations.
The SBS, or the Special Boat Service, mainly recruits from theRoyal Marines, a part of the military already considered to be an elite force.
Despite its secretive nature, the SBS began during WWII as a specialist Army unit trained to undertake difficult amphibious operations.
The primary role of the SBS is to gather information regarding targets, ascertain the direction of naval artillery fire, and to operate as a maritime counter terrorism unit.
In the service’s infancy, men would work in pairs, paddling ashore on small vessels launched from submarines in order to sabotage enemy rail and communication lines.
They would also plant mines on enemy ships, using their ability to work undercover and utilise the element of surprise as their means of doing so.
The SBS still plays an active, although a very secretive, role in military operations; they have most recently served in Afghanistan and Iraq.
Whilst in Afghan, reports surfaced of an SBS raid in which they rescued two Italian soldiers who had been captured by the Taliban.
Sadly, in 2012 the SBS failed in their operation to rescue British hostage Christopher McManus and his Italian colleague when they were taken as captors in Nigeria.
Unfortunately, both men were killed by the gunmen who held them.
Unsurprisingly considering that both organisations believe themselves to be the world’s elite military forces, a long-standing rivalry exists between the SAS and the SBS.
But there's no doubting that the Special Boat Service have to undergo one of the toughest selection processes on the planet.
Beginning with four weeks of endurance testing, this is designed to "weed out" anyone without the required level of fitness.
The endurance testing ends in a 40km march to be completed in under 20 hours, whilst carrying heavy bergens.
They will also undergo jungle training which is designed to push the recruits to the limits of their endurance, as they are forced to navigate, patrol and survive in the dense jungles of Belize.
Arguably the toughest element of the process is the four-week combat survival course.
Here, troops will be lectured on escape and evasion techniques before embarking upon exercises where they were 'captured' by enemy troops and subjected to intense interrogation.
Here, they will be deprived of food, water, and sleep, placed in stress positions and subjected to intermittent blasts of white noise, after which they will be interrogated.
Aside from providing their name, date of birth, serial number and rank, they may only answer questions with the reply 'I cannot answer that question'.
The final stage of training is the Swimmer Canoeist Training Course, which focuses on the skills particular to the SBS, primarily underwater demolitions, beach reconnaissance and surveying techniques.
The primary vessel which the SBS use in carrying out their top-secret operations continues to be the canoe.
This small boat provides the perfect means for gliding silently through the water, unseen and unheard by the unsuspecting enemy.