It's amazing what you can find hidden in Wikipedia:
On 21 August 1967 four A-6 Intruders from the carrier USS Constellation (Squadron VA-196) attacked a railway in North Vietnam, one A-6 piloted by CDR Leo Profilet and LCDR William Hardman was hit by a surface to air missile (SAM), their aircraft cartwheeled, and both crewmen ejected, becoming POWs. The three other A-6s continued their mission, then suddenly two of the three Intruders became separated from the third aircraft, and possibly due to the thunderstorms and low clouds, headed directly across into Communist China. They were attacked and shot down by Red Chinese Mig-19s (J-6s). LTs(JG) Dain Scott and Forrest Trembley, and LCDR Jimmy Buckley did not survive. LT Robert Flynn became a POW, and was repatriated on 15 March 1973.