I played mission 27 about a dozen times and I can't seem to get an S rank. For OS I use Javier and Jess, for BM I use Grit and Hawke, and for Green Earth I use Sensei and Eagle. I get 100's on both speed and technique but I get horribly low scores for power. The last 2 times I got a 42, then a 20. I thought the definition for power is that it depends on how much enemies that you kill in 1 turn. I killed the 2 med tanks, the neotank, and artillary/infantry in 1 turn but I still get low scores. I even tried destroying a lot of the structures in one run but that didn't work either. Someone please give me some advice!!

Difficulty matters, for Normal Campaign and hard I used different COs.

NC:OS: I use Javier and Jess, no tagging just push Javier's direct defence up using skills also for mobility use prairie dog and pathfinder, give Jess Teamwork, Bodyguard and Synergy.

BM: Colin and Sasha, Either use Colin for units that cost almost nothing or Sasha to stop Vonny from using his SCOP, whichever path you take use all the money skills on the main CO and the same skillset as Jess on the other CO.

GE: Eagle with Sami, give Sami the same skillset as Jess, for Eagle do whatever to make him stronger.

HC: The only change to Hard Campaign is the OS COs, Kanbei with all defence skills and Sonja with the same skill set as Jess.

Sacrifice your starting Megatank, break the cannons and rush'em.