TM 9-2320-280-20-2 page 7-22 clearly calls for "silicon based brake fluid". Sounds like DOT 5 to me.
DOT 5 is silicone based brake fluid, is less common and does not scavenge for water the same way as DOT 3, 4, or 5.1. DOT 3 and 4 are more common, are glycol based, and scavenge for water by...