Build a Nuke Silo as either Allies or Soviet. When the Nuclear Bomb is ready, sell your Nuke Silo, and immediately target the Nuclear Bomb somewhere. The Nuke Silo will partially sell giving you credits and a group of 5 random infantry (but the Nuke Silo will not disappear!), and the Nuclear Bomb will also explode where you targeted it. The good part is that the Nuke Silo will cancel selling itself, so you can keep on doing this trick without having to build more Nuke Silos. This will work much easier under slower game speeds.

Infantry can literally walk on water. Put a Transport by the shore and an infantry unit nearby. Tell the infantry to enter the transport, but just before he enters, move the Transport away from the shore. The man will continue to walk on the water. You can then tell him to enter the Transport again, and move it away just before he enters. This way you can get infantry to move anywhere on water, including getting a spy into an enemy subpen which is surrounded by cliffs. Note that if you try this trick with a land vehicle, it will sink, so don't waste your money!

During a single player game, if you are running out of ore, simply save the game and then reload it. The ore will magically re-appear.

A naval unit can be repaired by telling it to return to a naval yard or subpen. While it is docked for repair, if you order it to attack a spot out of range it will move to get in range but will continue repairing on the way!

Build a Telsa Coil and a Mammoth Tank. When they are both completed, decide where you are going to place the Coil. Tell the Mammoth Tank to got there. Just before the Tank gets there build the Coil. The Mammoth Tank will drive right onto it! Now you have a Telsa Coil structure with AA and AG missles, 2 120mm cannons and self-healing heavy armor! The only downside is that once the tank moves off, (usually by accident) you cant get it back on. Also, you cant repair the coil until the tank is off.