Unfortunately, no. You can "build" a SingleMission with the player sub as a group leader, and you can add ships to said group. However, it will not "Save" as such. If you instead make the submarine non-player controlled, the mission will save OK. You can then go into the file in a text editor and change the control of the sub back to the player, and the mission will show on the menu. However, your submarine is now "Unknown", and the scenario will not load.
My guess is that as soon as you go to dive, any surface ship will attempt to dive, and be destroyed... or it will not allow you to submerge, or whatever might happen. But I have tried multiple ways to get this to happen, and thus far, no success... It would be really nice to have destroyer escort when you leave Pearl, but alas, the only way to do it is to "guess" what the player might do as they leave... I have tried spawn triggers, which do function as intended, but if the player goes faster or slower than their escort... well, it can "look" rather odd - if they even go in the direction their "orders" tell them to...
