[DRG]

OK, further testing indicates that you may have stumbled onto something.... or not. Any of those boats given MC0 ( default ) will behave the same way as one given UC5 so in this case what you may have discovered is when the game is given a MC it has no information on it treats it as default. That would be typical safety code

That said, MC6 also works like default but produces the same sound FX as the assault boats and boats given MC6 also follow the river and don't ground out on shoals