7 months at sea with HMS Duncan comes to an end with a tense stand-off against Russian warships which are threatening to fire on them if they launch missiles into Syria. Meanwhile, Danny goes for promotion and Liam is disciplined.
The frigate HMS Northumberland prepares to leave port for a 4-month deployment with a crew of 220. Huge amounts of food are loaded onboard along with the ship's new chef, but a fire nearly undoes the entire mission before it's begun.
H.M.S. Duncan is ordered to the Straits of Hormuz after Iranian forces take control of the British flagged tanker Stena Impero and hold the crew hostage.
The ship is heading towards Crimea, when a Russian ship HMS Duncan is tracking disappears. The crew discover that the missing ship is a spy vessel and the Russians are also tracking them. As they approach Crimea, the situation escalates.
Reports that a chemical weapon has been used in Salisbury changes the mood on-board. The crew is on guard as it heads towards Montenegro when a chemical attack in Syria sees the Duncan go to action stations.
HMS Duncan joins Operation Inherent Resolve, protecting a French Aircraft Carrier off the coast of Syria. The ship detects a Russian submarine and a mystery helicopter, then receives top secret orders to help evacuate 33 trapped Britons.
Heading out to the Med and the Black Sea, the 280 men and women onboard face a heart attack, a man overboard, and a show of force from Russian airplanes.
HMS Duncan has a long journey ahead of her as she receives orders to support a French aircraft carrier on campaign in the Middle East. A female lieutenant training to become captain is given full control of the warship for 24 hours.
HMS Northumberland is deployed off the west coast of Ireland and receives intelligence that a Russian warship has been spotted heading towards Faslane.