For my son's 6th birthday, he asked for a Tank/Military Birthday Cake. I thought a tank cake would be perfect. I scanned through this website to get ideas as well as searched the web for pics of real military tanks. I tried to keep it simple - and though I originally wanted the entire cake to be one big tank, resorted to more of a military scene that incorporated a tank (I was short on time).
The base of the cake was made from using a roasting pan and 2 box cakes - basically the same as using two 13x9 pans put together - except there's no gap that has to be covered up. Then I made another 13x9 and cut it up to make the tank. It was that easy- just put a few squares of cut cake together in various sizes and shape a little. I did cook the cakes a few days prior and froze them by wrapping in siran wrap then aluminum foil. Freezing them makes icing them SO much easier and I think it adds a little moisture to the cake as they were so moist the day of the party.
I used chocolate icing for the base and a butter cream that I mixed green, purple and brown together for the tank. I used a Oreo cookie stick for the large gun of the tank, real Oreo cookies for the wheels and I rolled out black licorice for the tracks (I actually got a lot of compliments on the tracks). I let my son put some washed toys on the cake to complete it (including the toy gun on the very top of the tank) -- and he loved it! He was so proud that he helped make it!
My original plan was to cover the tank in fondant, but I forgot to sift the powdered sugar so the fondant was way too lumpy to use all over. I did manage to salvage a little and using black gel, made the little black utility boxes on the tank (and to support the large gun). Even though it turned out quite differently than I had intended, it was easy and fun and most importantly, my 6 year loved it.