On July 19, 1969, Senator Edward Kennedy drove his vehicle off a low bridge on Chappaquiddick Island in Massachusetts. The vehicle sank in 2.1 m of water, coming to rest on its roof. According to Kennedy's version of events, he managed to escape from the submerged vehicle without injury, but his female companion, Mary Jo Kopechne, drowned without any sign of injury. He did not report the accident to police until 10 hours later. Kennedy's version of the events was widely disbelieved but was never seriously challenged by the local police or accident investigators or at the subsequent inquest. The accident effectively put an end to Kennedy's bid for the presidency of the United States. At least a dozen books have been written on the subject, offering alternative explanations but the physics of the accident itself has never been properly investigated. In this paper, experiments using a toy vehicle are described where the vehicle was projected into a container of water to investigate how the roof may have been damaged. The trajectory through the water was filmed and is explained in terms of elementary physics. Further investigation could be the subject of student projects and would provide an interesting introduction to forensic physics.