The battalion was initially deployed to Cape Paerata, New Zealand in February 1943 and then moved to Guadalcanal in July of that year.

At Iwo Jima, 3/9 had the distinction of making the only battalion size unsupported, non-illuminated night attack against the Japanese in the Pacific War.

Attesting to the ferocity of combat on Iwo Jima, all 22 of the battalion's officers who landed on D-Day were killed or wounded by the end of the battle.

[3] Kilo and India companies were deployed to Bien Hoa Air Base to provide ground support, for Marine Aircraft Group 12 (MAG-12) in May 1972.

[5] 3/9 was the Battalion on Float at the time of Operation Frequent Wind, on Mount Fuji, Japan doing cold weather training went the call came.

They had to be flown back to Okinawa and loaded onto USS Denver and were involved with the evacuation of the VIP's and refugees until the very end.

During 1986 the battalion participated in the filming of Heartbreak Ridge in Camp Pendleton, California and Hamburger Hill while deployed to the Philippines.

They were sent on patrols and participated when fired upon and they would defuse land mines placed around friendly villages who supported the Honduron Military.

On 23 April 2011, while conducting combat operations in Helmand province, Afghanistan, LCPL Dominic Ciaramitaro and SGT Sean Callahan were killed in action.

The Marines and Sailors of 3/9 were successful in breaking through and pushing back enemy lines, ultimately removing the Taliban from power and handing over the area of operations to the Afghan National Army (ANA).

In October 2012, 3rd Battalion 9th Marines deployed to Marjah, Helmand, Afghanistan in support of Operation Enduring Freedom, returning in May of 2013.