The tonnage bar doesn't fill completely up - see this post

http://www.subsim.com/radioroom/show...42&postcount=3

If it looks like this then you have reached the required amount. If it's not going up at all then you are sinking ships in the wrong area (or possibly the wrong kind of ships)

Hope this helps you matey.

i am sinking ships in that area. what ships i am supposed to sink?

It depends on your mission orders. If you are on the first mission then as far as I can remember any merchants will do. You need to be in the right area I.E. the right side of that red line - you should see a patrol icon that shows you where (yellow box)

I've been going up and down the line and got 200k tons and i haven't got any progress AT ALL on the mission.