This is done in the second mission of the fifth war story, "Young Men's Work". This was recorded on easy difficulty; however, difficulty does not affect the achievement / trophy. Simply follow the guide to find the three officers and be sure to kill them with melee attacks. Do not worry about being spotted or alerting the enemies.
Here is a video guide with English commentary for this achievement!
Here is a playlist of guides for this game!
https://www.youtube.com/playlist?list=PL-HeW6XkKdUIicZXsqAK5...