First off, get your transports to the Pentagon ASAP. You need to get your base up and running quickly (as is generally a good idea) and begin taking measures to clean up Washington. As you are working, try to keep the prism towers well repaired as they will take shots from the tanks that attack. One tank isn't much threat, but they can gradually wear down the towers. Replacing them is more expensive than trying to save them. The Pentagon can be garrisoned when your prism towers eventually fail (they probably will) concentrate the troops near the southeastern corner of the building where the enemy troops are coming in. There is a good building to garrison north of the pentagon to prevent the enemy troops from entering your base from that direction as well. You can also station a small group near the bridge to slow them down. Build plenty of grizzly tanks here. The Soviets are building more rhino tanks nowadays and you need to make up the difference in power.

After scouting the areas with a rocketeer (who got shot down by a flak cannon) I discovered a small Soviet base over the bridge to the east of the Pentagon. I made a large diversionary attack force consisting of grizzly tanks and GIs and a few engineers to back me up. I had constructed a battle lab and now had access to prism towers. I made sure i had plenty of power and built a prism tower, but didn't place it on the map. I let it sit waiting until I had that zone of control around the Soviet base. I sent the attack force into the heart of the base, deploying the soldiers right there near the tesla coil. The force fought very hard, and my engineers were able to slip through. I captured the Soviet war factory and now had access to build my own Rhino tanks! More importantly I had a foothold in an area closer to the heat and could make reinforcements available faster. I also captured the construction yard and made an outpost of sorts with Soviet buildings.

I produced many rhino tanks to escort my GIs this time, and sent out rocketeers on patrol to eliminate resistance from small forces. They also eliminated a lot of engineers which may have posed a threat to my buildings in numbers. Otherwise, the push to destroy the rest of the Soviet forces was fairly easy after the first roadblock. This is a type of battle you should get used to, destroying bases happens a lot and there are many ways to do it. I can't tell you a perfect way as there probably is none. Just be aggressive when you feel confident and at least strive to do more damage than you take - cost them a lot of time fixing the damage you've done even if your attack fails.