To be selected for it is a great honour, a compliment to your skill, but there is also a great risk – as it has a high failure rate.
Pass the course and you go straight on to take a command role, but if you fail, your entire submarine career is likely over and you may never serve on a nuclear submarine.
The Royal Navy's 'Perisher' is recognised as one of the most intense military training schemes anywhere in the world.
Candidates are potential submarine Commanding Officers, chosen after reaching the highest position possible before taking command.
A highly experienced hand-picked former commanding officer, known as the 'Teacher', and his staff, rigorously test the students over several months.
The success or failure is decided by the Teacher, whose word is final with no second chance and no appeals.
The Perisher course was introduced by the Royal Navy in 1917 as formal instruction in submarine command.
Over its history, the brutal course has had a failure rate rumoured to be over 50%.
Much of Perisher, officially called the Submarine Command Course, takes place in classrooms and simulators ashore.
The highly experienced 'Teacher', and his staff rigorously test the students over several months – if they are not good enough then they do not proceed to the sea phase.
In the simulator, working with a team of experienced submariners, the students must learn to deal with any possible scenario they may face at sea.
Then, in the final sea phase, things become more intense with the students taking turns commanding a real nuclear submarine under the Teacher's supervision.
Students will be put through a series of high-tempo scenarios, including gathering intelligence from onshore installations and warships.
It is much more than a practical test, the students involved will have already proven their practical skills, or they would not have proceeded past the sea phase.
What is truly being put to test is their leadership qualities under high pressure and in stressful situations.
The main reasons for failure could be that the candidate may regularly lose situational awareness, or show a narrow focus or over-reliance on one tool or aspect of operations.
Making mistakes does not cause a student to automatically fail if the mistake is recognised and corrected before the submarine is endangered.
Students who fail the course are, in most cases, no longer permitted to serve on submarines in any capacity.
There is no stigma that follows failure, due primarily to the high failure rate and intensity of the course.
They will be given a bottle of whiskey and then advised on where their future career in the general service can lie.
In June, five students were put through their paces on the demanding Perisher course aboard HMS Artful.
One scenario saw HMS Artful act as the submarine threat for aircraft carrier HMS Queen Elizabeth during Exercise Strike Warrior with fellow Carrier Strike Group (CSG21) ships along with P-8A aircraft and Merlin helicopters playing the air and surface threats.
Three students successfully completed the course and were informed of their success with the famous words "Congratulations Captain".
After the stress and tension of the sea phase of the course ends, their skills and lessons learned will follow them into their next assignment as submarine Executive Officers, second in command.