I agree with you SeaQueen, MP scenarios must use some compromise.
Especially against mission duration.
Real ASW engagment takes hours, even days ... you just can't do that on a MP mission with DW.
But there is tools, able to compensate this problem.
Random location is the best one.
With them, you could still have the fewer possible range beetween platforms with a very large choice of initial position.
This way, you allow at least 15 mn before any detection could occurs, and nobody knows where the ennemy will come from.
On MP mission, this is a basic rule for replayability of a mission.
When creating a MP mission, you should spend most of the time not on creating the action, but on generating the randomless, preferably on speed, bearing and even course of the targets.
If you manage to do that correctly, each time you replay the mission, you shouldn't have more informations available than if you played it for the first time.
So the 2 main factors for MP games are
1) no more informations for everyone than if they played the mission for the first time
2) At least 15 minutes before any detection occurs.
Then you have lots interesting and "realistic" possible scenarios.
I made some scenarios I replay quite often, editing them will better show you the way I proceed to try to make this kind of scenarios.
you could find the latest versions here :
http://okof4.free.fr/missions/DW/