|“||You'll join K-Unit. We don't use names. I have no name. You have no name. If anyone asks you what you're doing, you tell them nothing. Some of the men may be hard on you. Some of them may resent you being here. That's too bad. You'll just have to live with it||”|
—The Seegeant informs Alex Rider of the hardships he will endure under his time in the K-Unit
The group consists of four men in a billet, though Alex became the fifth upon arrival, and was generally ignored by the group for the entirety of his stay. The four men are codenamed Eagle, Fox, Snake and Wolf, with Wolf being the leader.
Upon Alex's arrival, he was given the codename "Cub", though was regularly referred to by the soldiers as "Double-O-Nothing". Only Alex's and Fox's true names are currently known, Fox's being revealed in Snakehead as Ben Daniels.
In the book they are seen doing various training, such as in an area known as the "Killing House". Alex is the subject of bullying from Wolf in particular, who's attack on Alex in the Killing House lead to the Unit failing the exercise. In a bonus chapter of the novel Stormbreaker named RTI, the group are dragged from their beds for a RTI (Resistance To Interrogation) exercise, in which Alex escapes the building they're locked in by climbing through a drain before causing the vehicle the interrogators are in to fall off a cliff and freeing the rest of his Unit. The group later do an airdrop from a C-130 Hercules, in which Alex saves Wolf from being binned (kicked out of the SAS) by kicking him out of the plane after the man shows fear of jumping. After this, Wolf is less hostile to Alex next time they see each other.
Wolf appears later in the series as part of the squad who storm the Point Blanc Academy. He is reluctant for Alex to return to the school, though eventually agrees and is shot while protecting Alex from Eva Stellenbosch though he survives.
Fox later becomes an agent for MI6 and meets Alex in Snakehead, the two eventually leading a squad with the Australian SAS to storm Dragon Nine.
- In the film version of Stormbreaker, the names/members of K-Unit are changed from Wolf/Eagle/Fox/Snake to Wolf/Eagle/Fox/Bear instead.
- In the film instead of the Killing House scene being used, the scene from the bonus chapter is used instead: they fail a Night Navigation exercise and are locked up, but Alex breaks them out by climbing up the chimney and ultimately causing the trailer of interrogators to roll into a lake.