Operation Crimp

Operation Crimp (8–14 January 1966), also known as the Battle of the Ho Bo Woods, was a joint US-Australian military operation during the Vietnam War, which took place 20 kilometres (12 mi) north of Cu Chi in Binh Doung Province, South Vietnam. The operation targeted a key Viet Cong headquarters that was believed to be concealed underground, and involved two brigades of the US 1st Infantry Division including the 1st Battalion, Royal Australian Regiment (1RAR), which was attached to the US 173rd Airborne Brigade. Heavy fighting resulted in significant casualties on both sides, but the combined American and Australian force was able to uncover an extensive tunnel network covering more than 200 kilometres (120 mi).
The operation was the largest allied military action mounted during the war in South Vietnam to that point, and the first fought at division level. Despite some success, the allied force was only able to partially clear the area and it remained a key communist transit and supply base throughout the war. The tunnels were later used as a staging area for the attack on Saigon during the 1968 Tet offensive before they were largely destroyed by heavy bombing from American B-52 bombers in 1970, ending their utility.