Less than three years earlier, in August 1968, a Dac Cong sapper unit attacked the MACV-SOG compound outside Da Nang. The compound, home to command and control elements of SOG's Command and Control North (CCN), was considered a high-security facility manned by elite troops, but during the attack "a dozen Green Berets were killed, along with an unknown number of their Nung mercenaries." Coincidentally, one of the officers present at FSB Mary Ann had also been at the CCN compound when it was attacked. Sappers also attacked elements of the 101st Airborne Division (Airmobile) in March 1971 at the old Khe Sanh Combat Base. Opened to support ARVN operations in Laos during Operation Lam Son 719, Khe Sanh contained a number of fuel storage locations and maintenance facilities for helicopters. The sappers took losses, but reached the runway and demolished both ammunition stores and fuel tanks. Similar attacks took place against Firebase Crook in 1969 and Firebase Illingworth in 1970.