| 3rd Battalion, 9th Marines | |
|---|---|
 3/9 Insignia | |
| Active | 20 November 1917 – 12 August 1994 21 May 2008 – August 2013 |
| Country |  United States of America |
| Branch |  United States Marine Corps |
| Type | Infantry Battalion |
| Role | Locate, close with and destroy the enemy with fire and maneuver, and repel the enemy's assault with fire and close combat |
| Part of | Deactivated |
| Garrison/HQ | Camp Lejeune |
| Nickname(s) | Shadow Warriors |
| Motto(s) | "Death in the Dark" (Vietnam Era), "Striking 3/9" (Post-Vietnam Era) |
| Engagements | World War II
Vietnam War |
| Commanders | |
| Current commander | None |
The 3rd Battalion, 9th Marines (3/9) is an infantry battalion of the United States Marine Corps. Formed during World War I it served until the early 1990s when it was redesignated as 3rd Battalion, 4th Marines (3/4) during a realignment and renumbering of the Marine Corps' infantry battalions, following the deactivation of the 9th Marine Regiment. The 3rd Battalion, 9th Marines was initially a subordinate unit of the 9th Marine Regiment, 3rd Marine Division, but was later operationally transferred to the 1st Marine Division as a subordinate unit of the 7th Marine Regiment where it remained until its redesignation as 3/4.
3/9 was reactivated under the 2nd Marine Division in May 2008 as the Marines expanded as a result of the continuing War on Terror.