The United Earth Joint Service was a military and exploration branch of Humanity from the planet Earth prior to their species' entry into the Systems Commonwealth. They were responsible for the launching of the Bellerophon Deep Space Expedition, under the command of Captain Fehdman Metis. During the Long Night and whilst on the Bellerophon, Rommie used Captain Metis's command codes to gain access to the ship's hangar, so that she could investigate a damaged Slipfighter stored there. ("The Lone And Level Sands")
The fate of the Joint Service after Earth joined the Commonwealth is unknown, although it was presumably disbanded and merged with the High Guard, possibly becoming Earth's Home Guard contingent.