I recommend the Trigger Maru Overhaul Supermod. It allows for varied mission objectives, and multiple new ones during your patrol (for example, the first objective is commonly to get to a point outside port and await further orders via radio)
For example, I got sent to Celebes, then had a photo recon on the way back to base. It was up to me whether I wanted to do it, of course. I'm not endangering my boat for some photographs of Medium Gun Boats
