a german abbreviation

[Tycho]

The German language is complete fog for me.
The button in the game imitate two things - flood the tube and open the door.
If look over "Torpedo launching procedures", I see:

Order:
Ready the tubes from I to IV for submerged shot
(Rohr I bis IV klarmachen zum Unterwassersehuß!)

Report to the control room:
Tubes from I to IV are to be flooded!The muzzle doors are to be opened!
(Rohr I bis IV werden bewässert! Mündungsklappen Rohr I bis IV werden geöffnet!)

Acknowledgement from bow torpedo room:
Torpedo tubes from I to IV ready for submerged shot!
(Rohr I bis IV sind klar zum Unter-wasserschuß!)

So, something with Mündungsklappen is right, but how to abbreviate it I don't know.