@Cmdr:
Forum rules state that if something is not corrected within one game turn, then it stays as is
Never heard of this before. Plus, he’s playing FTF, not by forum.
2 things come to mind.
First, after turn 4 everybody should be at war with everybody. Claiming an undeclared DOW is kind of a reach.
Second, and the rules are explicit on this, once you collect your income, it is immediately your opponents turn. After that, any changes made to the board (including missed combats, non-combat changes, hanging aircraft, etc) are at your opponents discretion. And, in this case, he has even more rules to back him up. Since no dice were rolled for attacking units and it is possible for a sub to enter a sea zone during a combat move and then submerge before combat he is perfectly within his right to make that assumption if the TP is still on the board at the beginning of his turn.
This is less of a rules issue and more of an etiquette issue.
You were being a rules dick about the DOW and he was being a rules dick about the TP. Sounds like you’re both even.