HMS Achilles is an Astute-class nuclear fleet submarine of the British Royal Navy commanded by Sean Ramsey, leader of the Immunes. The sub cames into conflict with the USS Nathan James (DDG-151) throughout season 2.
After learning they are immune to the Red Flu, Ramsey began believing immunes were destined to inherit the world. Ramsey and his brother Ned trained a crew of mercenaries also immune to the virus to operate the sub and started using Achilles as a floating base of operations. In his attempts to destroy the cure, Ramsey and his crew came into conflict multiple times with the Nathan James knowing the cure is on board the ship, but never ended with either side sinking the other. In S2E12 in a final battle with the Nathan James, the Achilles was finally sunk by combine fire from the James' 5/62-Mark Naval Gun and a shore battery commandered by Mike Slattery leaving the crew dead and Ramsey trapped on bottom of the ocean.
Originally in the service of the British Royal Navy, while at sea a lieutenant became infected with the Red Flu. The virus quickly spread throughout the sub, killing nearly everyone on board. Being immune to the virus, Sean Ramsey and his brother Ned where the only ones to survive. The brothers then found other immunes and trained a new crew to operate the sub.
According to the real-life Astute-class technical features, the Achilles has a length of 318 ft (97m), beam of 37 ft (11.3m), and a draft of 33 ft (10m). Achilles is powered by Rolls-Royce PWR 2 reactor and fitted with a pump-jet propulsor, and MTU 600 Kilowatt diesel generators. It can go at a speed of up to 30 knots (56 km/h) submerged, and has a test depth of over 300m. More than 39,000 acoustic tiles mask the vessel's sonar signature.
Its nuclear power-plants allow Achilles to stay at sea without ever having to refuel, only being limited by food and maintenance requirements.
The Achilles has stowage for 38 weapons and would typically carry both Spearfish heavyweight torpedoes and Tomahawk Block IV cruise missiles. The Tomahawk missiles were used on S2E5 to destroy the cure labs on land. The sub's Spearfish torpedoes were used in S2E5, S2E10, and S2E12 against the Nathan James. The sub is also fitted with a dry deck shelter, which allows special forces to deploy while the submarine is submerged. It is used by Ned Ramsey and his forces to board the hospital ship Solace on S2E4.
The Achilles is equipped with the Thales Sonar 2076, an integrated passive/active search and attack sonar suite with bow, intercept, flank,and towed arrays.
- Since an Astute's Tomahawk missiles only have a range of 1,240 miles, Achilles' missiles couldn't have reached all the cure labs in America.
- Though Achilles appears as an Astute submarine on the outside, it's interior is actually based on an older submarine.