Well, looking back at this map, I say that there was a trick they put in. There were a few things such as the attack on where they go as well as 2 battleships. This could be a bit more difficult as Colin, so I decided to see if I can beat this as Kanbei and long and behold, here's a video attempt!
Follow me on: twitch.tv/merable08
Edit:
From what happened, it IS still possible as Colin! Segrald made a video with save states, which is here:
https://www.youtube.com/watch?v=RC_Bgw6X1Kg
'THINK Grim Guy', AKA, N.H, AKA, BIG BRAIN Grim Guy :P, was able to not only beat it, but ALSO get an S rank, something I thought it was impossible!
https://www.youtube.com/watch?v=L8QI2j5nHpo