Welcome, Corporal Clegg. I mostly agree with axisroll’s comments and Baron Munchhausen’s comments above – any time you add complexity to this game, you have to think about what you’d be willing to trade away. Would you scrap dogfights? Carriers? National objectives? Friendly neutral powers? Nothing? If you choose nothing, it probably means adding several extra hours onto the play time, which could be the difference between finishing your game at 8 pm and going home satisfied, or failing to finish your game at midnight and going home frustrated and tired.
One way to preserve the essence of your ideas while minimizing the added complexity might be something like:
In land battles, whenever any unit rolls a 1, you can choose to kill an enemy tank. In sea battles, whenever any unit rolls a 1, you can choose to score a hit on a carrier. In all battles, you can roll only 20 dice per round of combat – so if the Germans invade Moscow with 30 units against a defense force of 21 units, both sides will roll 20 dice in the first round of battle, but in the second round of battle, the Germans will probably still be rolling 20 dice, and the Russians will probably be down to 14 or 15 dice.