The recruits work in pairs as they tackle the threat of chemical warfare and execute a fast-paced extraction in near-freezing water. Then it's time for brutal hand-to-hand combat.

The seven remaining contenders spend 48 hours undergoing the most psychologically gruelling stage of the training, designed to test their ability to resist interrogation. The recruits are hooded and exposed to endless white noise, and face brutal tactical questioning from a specialist team, while those who endure this experience face an even greater challenge on the highest point on the island.