December 17, 1967: Prime Minister of Australia Harold Holt vanishes while swimmingDecember 15, 1967: 46 people killed in collapse of West Virginia and Ohio's Silver BridgeDecember 3, 1967: Dr. Christiaan Barnard performs first human heart transplantDecember 8, 1967: USAF Major Robert H. Lawrence, Black astronaut, killed in F-104 crash