Yes, your Uboat Missions Add-on should work over a LAN or a WAN. The LAN is easiest, if you're both on the same network, since the game has its own network interface. You do both have to have the same ~EXACT~ game. Same mods, too. I haven't been able to get my sons to play lately (they don't like being sunk and get bored to tears while I'm maneuvering into position to take 'em out)...

- I'm not sure how you'd set up a Hamachi connection for it, but:
http://www.subsim.com/radioroom/showthread.php?t=142652
https://steamcommunity.com/app/15200...1475491118000/
couple of quick hits. I'll let you decide after an internet "Search" if you want to trust some of the other links I found...