In this episode, JJ is deep in the Devon woods with latest troop of Royal Marines recruits attempting to earn the coveted green beret, as they come under heavy fire on a tactical training exercise.On board giant aircraft carrier HMS Prince of Wales in the North Sea, Julia gets a chance to steer the biggest warship in the fleet. And she heads below decks to meet the sailors who live in one of the ship's largest shared sleeping quarters and discovers what it's like to live on a warship as the women prepare for an inspection.As well as the Royal Navy's surface fleet, some of its most important and clandestine work happens beneath the waves. Reporter Rob Bell is given special access to spend four days on board HMS Trenchant, one of the UK's nuclear armed submarines, as its crew prepares for an upcoming top secret deployment. It's a tense stay on board, as the crew are forced to dive to evade a foreign warship, and Rob is taken inches away from the submarine's nuclear weapon arsenal.Back on dry land in Portsmouth, JJ steps on board a landing craft that played a crucial part in the allied invasion of Europe on D-Day.It's here that JJ also explores the oldest and probably most famous ship in the navy's fleet – HMS Victory. She's the ceremonial flagship of the Royal Navy and perhaps surprisingly still has a commanding officer today. JJ steps on board and into the past to see what life was like for sailors in the time of perhaps the most famous Admiral of all time, Lord Nelson