| Marine Corps Special Operations Command Detachment One | |
|---|---|
 Marine Corps Special Operations Command Detachment One insignia | |
| Active | 20 June 2003–2006 |
| Allegiance |  United States of America |
| Branch |  United States Marine Corps |
| Type | Special operations forces |
| Role | Direct action, special reconnaissance |
| Size | 86 |
| Part of | US Special Operations Command |
| Garrison/HQ | Camp Pendleton, California, US |
| Engagements | Operation Iraqi Freedom |
| Commanders | |
| Colonel of the Regiment | Robert J. Coates |
The Marine Corps Special Operations Command Detachment One, also simply known as Det One, was a pilot program of attaching a permanent unit of the United States Marine Corps to the United States Special Operations Command. It was commanded by Col. Robert J. Coates, former commanding officer of 1st Force Reconnaissance Company. Det One was activated on 19 June 2003 and had its headquarters at Camp Del Mar Boat Basin in Camp Pendleton, California. It was disbanded in 2006 and succeeded by the permanent United States Marine Corps Forces Special Operations Command (MARSOC).