Cheats for Total Annihilation 

In Total Annihilation, press Enter for the message box, and then type in the cheat codes. Except for RADAR, they only work in multiplayer (if allowed) or skirmish games.
+ATM - Gives you 1000 metal and energy.
+CDSTART - Starts CD Music.
+CONTOUR# - Displays a 3D contour, # = 1-15.
+CONTROL# - Lets you to control a different skirmish AI.
+DITHER - Dithering instead of line of sight.
+DOUBLESHOT - All weapons do twice the damage.
+HALFSHOT - All weapons do half the damage.
+ILOSE - Causes you to lose.
+IWIN - Causes you to win.
+NOENERGY - Drops your energy to 0.
+NOMETAL - Drops your metal to 0.
+NOSHAKE - Stops explosion screen shakes.
+NOWISEE - Full map and disables line of sight.
+RADAR - 100% radar coverage.
+SING - This command makes units "sing" when given orders.
+SWITCHALT - Allows you to switch between squads with alt+# keys.
+VIEW# - Lets you see how much metal and energy a player has. 
Below is the first Campaign cheat code:
Click on Total Annihilation's Single Player icon. When the Single Player Game page appears type DRDEATH (it is not case sensitive). This will cause a Cavedog Entertainment bone to appear between the Load Game and Previous Menu icons on the right side of the screen. Clicking on the bone will take players to a special Play Any Game screen where they can play any Total Annihilation mission, even if they have not earned their way to that level yet.

Cheat:
If you are defeated in battle you may still move on to the next battle. The next battle should be selectable in the battles menu. Just click and start. 
Hints:
The last battles of the game are relatively easy if you are Arm. Just build tons of mines, tons of collectors/reactors/geo-powerplants, add about 3 of every type of unit construction building. Set them all on en masse and move the 'new unit location' to somewhere else (it gets crowded). Attack the doomsday weapons with merls. Merls can fire outside D.day range and the weapon does not need to be visible. Because you can see all wreckages you can attack with some Merls and an advanced radar. You also hit the 200 max unit limit.
Your units also get stuck around the battlefield because of wreckages. This is really crippling in narrow sections. Have a few construction aircraft hovering around to help out in the clean up.