At the title screen, hold [Left Shift] and click on the round speaker.
View credits
At the title screen, click on the Westwood logo.
Free men
Build a missile silo. Then, when the missile is ready, sell the silo and immediately launch the missile. If done quickly enough, the sale will have stopped and some troops will come out of the silo.
Tesla tanks
Select a skirmish or multiplayer game. Then, choose to be France and have a Tech level of at least 7. Now before building a radar jammer, hold [Shift] and click on the radar jammer icon.