An EC-121R, 67-21495, callsign “Batcat 19”, 554th Recon Sq, Korat RTAFB, was scheduled for a combat tactical mission. Takeoff was initiated at 16:25 UTC, September 5. The flight to and within the combat area was uneventful, except for structural and engine icing which was reported as being light to moderate in intensity. Due to these icing conditions, Batcat 19 changed altitude a total of six times. Batcat 19 reported leaving the combat area the next day at 03:56 UTC for return to Korat with an estimated time of arrival of 05:15 UTC. Batcat 19 made initial contact with Korat Approach Control as he was approximately fifty nautical miles east of the airport. The aircraft received radar vectors and descended to twenty-three hundred feet indicated altitude for a precision radar approach. He was thirteen nautical miles northeast of runway 24 when in position to begin his approach. The aircraft, during the approach, drifted left of course, and at a point between one mile and two miles from runway 24 executed a missed approach. When queried by the Ground Control Approach (GCA) final controller as to the cause of the left drift, Batcat 19 reported as “We were just having a little trouble in the rain out here”. Batcat 19 remained under radar control, completed a right closed radar pattern, and received vectors to a point approximately eleven miles on the final approach course for runway 24. The approach lights were turned on to maximum brilliance along with the sequenced flashing lights (strobe). The second precision approach appeared routine, with the aircraft generally on course, holding slightly above glide path until approximately one nautical mile from touch down. At decision height, the aircraft started dropping down through the glide path. The aircraft initially impacted the approach lights three thousand feet from the end of runway 24. It then struck the ground and eventually came to rest 1400 feet from the runway.