I would hazard a guess merc4ulfate, that the tonnage to sink may have been 10,000T of any type. It may have also have been a 5,000T of any type, and the merchant was 4,950 ton. I have had that happen entirely too often. Sneak into the middle of a convoy, get hits on two merchants, and only the little one sinks. Then the escorts hold me down the next few hours and the rest get away... If I think about it again, I might try to add a tonnage figure into a mission objective message somehow, yet not make it too obvious.
btw: Those "Sink" missions, where you are told to proceed to a certain location and standby for further orders, then they tell you to conduct anti-shipping operations, or search and destroy enemy shipping, none of those are area restricted in FotRSU. Once you have arrived at the location and gotten the "Captain authorized autonomy..." message, you can freely roam and hunt... The Patrol missions have to stay within a given area, which should be stated in all of the missions' orders - should be...
