I checked the file and the text was correct. However I drew inspiration from your post and took the key line from emergency surface and swaped it with the deck gun selection. I loaded up my game, and sure enough F10 would not cause the boat to emergency surface, but E will allow me to select the deck gun
I got tired of having to pull along side the merchant ship in darkness and take out their cannons with my 37mm before destroying it with the deck gun. Was tedious and dangerous work.