The Tan Son Nhut C-5 accident refers to the 4 April 1975 crash of Lockheed C-5A Galaxy serial number 68-0218 participating in Operation Babylift. The C-5 crashed on approach during an emergency landing at Tan Son Nhut Air Base, South Vietnam. The cause was ascribed to loss of flight control due to explosive decompression and structural failure. The accident marked the second operational loss and first fatal crash for the C-5 Galaxy fleet. It is also the deadliest accident involving a U.S. military aircraft.[citation needed]