The Naval Criminal Investigation Service (NCIS) was established on December 14, 1993, following the dissolution of its predecessor agency, the Naval Investigative Service (NIS), due to the fallout from the Tailhook scandal of 1991. This scandal occurred during a reunion of Naval Aviators, known as the Tailhook Symposium, held in Las Vegas, where numerous female civilians and military personnel were sexually harassed and assaulted by officers and enlisted staff.
The investigation into these incidents was mishandled, resulting in severe consequences for some Navy personnel, including ruined careers, early retirements, and letters of censure (administrative action, and the letter is placed in the official service record and is often seen as derogatory material for a promotion or assignment board to consider) that tarnished their official records and impacted future promotions. In response to the scandal, Congress enacted new legislation, leading the Department of Defense to restructure the Investigative Service into an independent organization led by a civilian Director with its ranks made up of an equal mix of civilian and military investigators.
The investigation into these incidents was mishandled, resulting in severe consequences for some Navy personnel, including ruined careers, early retirements, and letters of censure (administrative action, and the letter is placed in the official service record and is often seen as derogatory material for a promotion or assignment board to consider) that tarnished their official records and impacted future promotions. In response to the scandal, Congress enacted new legislation, leading the Department of Defense to restructure the Investigative Service into an independent organization led by a civilian Director with its ranks made up of an equal mix of civilian and military investigators.
Character of Gibbs was introduced in the JAG episode "Ice Queen" that aired Apr 22nd 2003. The episode was a backdoor pilot for the spin-off series NCIS.
The USMC CID (United States Marine Corps Criminal Investigative Division) is essentially a "Base Detective". The role would be equivalent to a Military Police Investigator in the United States Army. The CID can inquire into Misdemeanors and Felonies, and if the investigation does not fall into their purview, lack the subject matter expertise or outside their scope of jurisdiction , the preliminary work-up can be passed off to NCIS as per their Memorandum of Understanding of 1999. The Army CID, as well as the Air Force Office of Special Investigation (OSI), however, is equivalent to NCIS. The investigative arm of the respective services are co-located at Marine Corps Base Quantico in Quantico, Virginia.
When NCIS was originally the Naval Investigative Service (NIS) it was part of Naval Intelligence, and was led and staffed by both military and some civilian personnel, much like the Army's Criminal Investigative Division (CID). The NIS was commanded by a one-star rear admiral who reported directly to the Chief of Naval Operations and the Secretary of the Navy, making the agents part of the military chain-of-command. Which presented problems when investigating cases of wrongdoing on the part of officers, especially high ranking ones, who could use their rank to influence an investigation. Which was why NIS was restructured into NCIS and made an entirely civilian organization, with a civilian leader, that operates outside the military chain-of-command. This was primarily done because of the Tailhook scandal involving several high ranking Naval and Marine Corps officers (including a few admirals & generals) being accused of sexual harassment and conduct unbecoming an officer at a Naval Aviator symposium in Las Vegas. These officers, and the CNO, used their authority to obstruct the NIS investigation into the matter which directly led to it being restructured into a civilian organization.