The Royal Marines are the world's most elite amphibious force.
The reasons behind this go back to the foundation of the Royal Marine Corps and the purpose they have served ever since.
Since 1755, the corps has been in continuous existence as a distinct and separate part of the Naval Service, with Royal Marines ranks reflecting this separation.
On 29 April 1802, King George III recognised the loyal service of the corps by directing that they should be styled 'Royal' and the white facings on their scarlet coats were replaced by the blue of a royal regiment.
Although Marine Artillery Companies were formed in 1804 and the Royal Marines were designated a Light Infantry corps in 1855, it was not until 1862 that the corps was formally split into the Royal Marine Light Infantry (RMLI) and the Royal Marine Artillery (RMA).
The former wore infantry-style uniforms with scarlet tunics, while the latter wore artillery-style uniforms with navy blue tunics.
Watch: Royal Marines take part in essential marksmanship training.
In 1923, the two arms of the corps were re-merged to once again become the Royal Marines.
It is this status as infantry, setting them apart from the rest of the Navy, which is likely the cause of the differences.
To distinguish Royal Marines from their Army colleagues, their names are followed by the words 'Royal Marines' or 'RM'.
All Royal Marines officers, recruits and reserves are trained at the Commando Training Centre, (CTCRM), at Lympstone in Devon.
There are two distinct tiers, commissioned officers and other ranks.
The term 'officer' refers to someone with a commission, which is a formal document of appointment signed by the monarch.
Cover image: 40 Commando Royal Marines conducting strikes during Exercise Green Dragon (Picture: MOD).