Watch out for Mines and Subnets since you're playing TMO, I was pretty new to SH IV when I first put on TMO, was going ahead standard at periscope towards a port and suddenly all hell broke loose as my bow was sticking 15 feet in the air and was flooding heavily

If you play with the 3rd person camera available you can search ahead if you think there's a net, they extend pretty far but have a decent opening in them. As for mines, I still have yet to befriend one.