User dxdydzd has put together an amazing youtube playlist showing a minimum turn-count S-Rank run of the entire campaign. Each one of the map playthroughs match or beat the current “lowest turn counts” for each of these missions. For some maps with alternative best turn counts (e.g. Snow Hunters with/without the Lab Map), both routes are shown, too!
You can watch it below, or here from this direct link.