Don't think you can get both of those in the same game, but...
For tank action there is plenty out there. I prefer turn based stuff over real time. www.battlefront.com has the Combat Mission seriers which is "wego" - each side plots their moves and then you watch the action for the turn.
Dated, but free at www.matrixgames.com used to be Steel Panthers World at War.
As for naval? Also at matrix for free is Grigsby's old PacWar. And at battlefront they have Strategic Command which is WWII Europe with army level units and naval - a fancy version of Axis and Allies in a way - you can download a free demo.
Also at Matrix is the improved The Operational Art of War III which can do battles from Napoleon to future with units primarily division but also lower level and has generic battleships, cruisers, carriers, and other ships.
Over at www.theblitz.org they have numerous ladders and forums to explore and see what you can find a lot of opponents with.
Good luck in your search sir...
BvB
MajGen, 2/VIII/AoS
"Beer! It's not just for breakfast anymore!"