I vividly remember my dad telling me a story about when he was flying Huey gunships in Vietnam (20th SOS Green Hornets). It was on a mission when their primary mission was scrubbed and a FAC had them roll in and kill water buffalo that the enemy was using as transport. This was the only mission he said he ever felt bad or had any remorse. Conversely, he said that on other missions (including one where he was directly responsible for over 100 EKIA and earned the first of 2 DFC's), the main feeling was relief that the good guys got out of there in one piece.