Press "m" for messages. It takes you to the captains panel (F12?), there are 3 tabs for the log, messages and orders.
Dunno about speed dropping to 0.
Are you in rough seas? Seen it happen then when upping TC.
If it's flying a rising sun, it's fair game. Liners and such are actually used as troop transports, theoretically making them combatants. Try surfacing near one; if they shoot at you, you can shoot back.
