Many people watch the TV program NCIS, but what does acronym stand for?

The acronym, NCIS, stands for Naval Criminal Investigative Service.

The Service grew out of the Office of Naval Intelligence (ONI) during World War I.

In 1966, the name Naval Investigative Service (NIS) was adopted to distinguish the organization from the rest of ONI.

But, it wasn't until 1992 the first civilian director was appointed and the name of the agency was changed to the Naval Criminal Investigative Service (NCIS).

The NCIS mission is to investigate and defeat criminal, terrorist, and foreign intelligence threats to the United States Navy and Marine Corps—ashore, afloat, and in cyberspace. Over 1200 Special Agents, 900+ civilian employees and 200+ military members work worldwide to secure the Department of the Navy (DON) from cyber attack, criminal actions, espionage, defection, and assassinations of US Naval personnel.

The television series was first aired (Originally as NCIS: Naval Criminal Investigative Service) on April 22, 2003, and continues in it's 14th season.

The program was a spinoff of JAG, another popular program about the US Navy.

In two programs, the cast of the original team of NCIS was introduced...Two episodes of JAG Season 8, "Ice Queen" and "Meltdown" serves as the back-door pilot of NCIS itself.

These JAG episodes introduced Mark Harmon as Gibbs, Michael Weatherly as Tony, Robyn Lively as Vivian Blackadder, Pauley Perrette as Abby, and David McCallum as Ducky.