GUNDAM OPERATION TROY

There seems to be a lot of confusion regarding this achievement. I can confirm that my solution has worked for multiple people, myself included.

I played the same level on EASY, NORMAL and HARD by achieving the New Type rank on each difficulty.

You can play any mission to unlock this achievement on, but for reference I got the achievement in the E.F.F. campaign on MISSION 05.

It is still unclear how to get the New Type rank to pop though. I got this rank by playing through the mission as quickly as possible and without dying (this is the most important part).

Please comment if you vote negatively. I will edit my solution to make it better.

After earning 3 "New Type" ranks on the same mission and not earning the achievement, I earned another "New Type" rank on a different mission and the achievement unlocked. I noticed that the symbol next to "Level" in the mission clear screen had changed. I believe that the level improves based on the rankings you get in the story chapters. I didn't have a ton of good ranks after playing through on hard as I died a couple times on each mission. After going back and getting the 4 higher ranks (3 on 05, 1 on easy 03 of the E.F.F campaigns) I earned the achievement. It would make sense, given the fact it's based on the evaluation "level", not the evaluation "rank". If you have anything to offer to further improve the solution, I'd be happy to update it.

Completing the missions without dying is the most important. Completion time may help as well, though I don't think this hurts your score much. Make sure you also get most of the kills. I didn't notice any big differences when I used melee, though I did refrain from getting ammo/health unless I absolutely needed them just in case this had some kind of effect as well.

This is for completing either 5 or 10 missions without dying. (Not sure how many I did at all but I'm positive it's either five or ten) And doesn't matter what story or order you do this.

This unlocked when I completed a mission on normal so I can assume difficulty doesn't matter either.

I had done what I have read both here and on other sites, all saying to do the levels without dying. But after that I had still not got the achievement, even with most of the levels completed with veteran rank.
So with this in mind I checked what was being said on the Japanese sites about this achievement, and they said the same but you need to have the rank 'New Type' on 4 or 5 levels. You also need to run through the level when you are a soldier, doing most of the kills with melee. (This you can do on easy difficulty.)
(But even they were saying it still wasn't unlocking.)
I know I had got the new type rank on at least one level, so I decided to replay some of the levels that you mostly play as a soldier.
And after doing two levels with a 'New Type' rank the achievement popped. (I think I only had 3 with this rank, maybe four.)
I hope this helps.