Complex sentence: He was offered a spot in the G.I. Joe team as a Ranger, and after he decided on the codename Beach Head, he joined, eager for the challenge being a member of the most elite force in the US military would bring.
Split into simpler sentences: He was offered a spot in the G.I. Joe team as a Ranger. After he decided on the codename Beach Head, he joined eager for the challenge being a member of the most elite force in the US military would bring.