“You need to know where the warships are, determine where they are going to be, and work out whether you can stay at periscope depth or must go deep.

former captain of HMS Turbulent, Commader Ryan Ramsey

Cdr Ramsey – who’s known as Teacher by his students – says the ‘at sea’ phase of the course tests the would-be commanders to the limit.

“It’s four weeks at sea 'at war' against a variety of ships, submarines, aircraft and troops – they must win - failure is not an option.

"The students develop the skills of command, leadership, strategy and tactics, as they learn to out think the enemy.”

For the first time since 1993, the Royal Navy Perisher students are carrying out their training aboard diesel-electric submarines. This is part of a new joint programme, in this instance allowing submariners from the Royal Navy, Netherlands and Norway to share their experiences – and also ‘play’ with much more opposition than on individual national Perisher courses.

Richmond has now completed her part in the submarine training and is at sea giving the Royal Navy’s navigators of the future an equally-thorough workout as they carry out specialist navigation training.

As for Westminster, she's due to sail into London from March 13 for a six-day high-profile visit to the capital.