Operation Strike of the Sword or Operation Khanjar was a US-led offensive in Helmand province in southern Afghanistan. About 4,000 Marines from the 2nd Marine Expeditionary Brigade as well as 650 Afghan troops were involved, supported by NATO planes. The operation began when units moved into the Helmand River valley in the early hours of July 2, 2009. This operation was the largest Marine offensive since the Battle of Fallujah in 2004. The operation was also the biggest offensive airlift by the Marines since the Vietnam War.

Helmand, also known as Hillmand, in ancient times, as Hermand and Hethumand, is one of the 34 provinces of Afghanistan, in the south of the country. It is the largest province by area, covering 58,584 square kilometres (20,000 sq mi) area. The province contains 18 districts, encompassing over 1,000 villages, and roughly 1,446,230 settled people. Lashkargah serves as the provincial capital. Helmand was part of the Greater Kandahar region until made into a separate province by the Afghan government in the 20th century.