Yep open the mission editor
From the file tab on the left click " Open ( normal mission ) "
Point it to the SingleMission folder and then to the mission you want to change ( assuming you have copied the Multiplayer mission over into SingleMissions )
Once you have the mission open
Click the " Mission " on top line then Parameters
Put the dot into Single missions ( should already be in Multi player )
Looking on the main map in front you can see the player subs
Click on one and press the keyboard " Delete "
Continue until only one player sub left
When finished click on file
Save ( Normal Mission
