In this final episode, JJ is put to the ultimate gruelling test at the Marine Commando Training Centre, where his military career began 18 years ago. Back then he passed with flying colours, and now, despite the injuries he sustained in Afghanistan, he decides to take on the Endurance Course once again. It's a punishing 6.5 mile run along muddy paths, bogs, tunnels and obstacles. But has this former Royal Marine still got the physical and mental strength to pass the test?

From intense training to high-tech weapons, JJ also discovers what the future of naval warfare might look like. The Royal Navy have a special department dedicated to testing the weapons of the future - Navy X. Run from a sleek warship, Commanding Officer Michael and his crew are pushing the boat out with the latest remote controlled technology. JJ is allowed to have a go at remotely driving an attack boat with a fully mechanised machine gun mounted on its bow, as well as discovering how remotely controlled drones are now being used in the front line of battles in Ukraine.

In the North Sea, Julia's time on the mighty HMS Prince of Wales is coming to an end. After successfully leading Steadfast Defender, the largest NATO exercise since the cold war, Julia helps the ship's crew as they prepare to enter a foreign port for the final leg of her epic journey.

From Britain's biggest and newest warships Julia heads to one of the most famous warships of the 20th Century, HMS Belfast. Now a museum on the River Thames in London, she's meets some of the ship's veterans to get a reminder of what life was like for sailors around the time of the Second World War.

The Mary Rose is one of England's most famous warships. Sailing for more than 30 years during the reign of Henry VIII, she sank during a battle with the French off the coast of Portsmouth. JJ heads to the museum to learn what life was like for a Tudor sailor and to discover how the ship may have met her fate.