I completed the scub showcase last night. I tried calling in the mortar strikes, That in itself took me forever to learn how to do. When the mortars hit the npcs were on me in an instant. I gave up that option after 2 tries. Went back to trying to sneak down prone, go to the vehicle and was able to get the rocket and sneak back.
Shooting down the chopper was easy. Getting back into the water and avoiding npc fire was tough. I swam down in the deep trenches thinking i might loose them but when i came back out at the evac point I had npc on the ridge killing my evac team. lol i'm just glad it completed.
Thanks to all for the helpful suggestions.