That's actually quite a small amount of the army they have when playing. Just playing the single player stuff, and went to attach a Chaos controlled land. Entered, built a base, tech'd up enough to launch Dreadnaughts and sent 5x Dreadnaughts and both Terminator squads in there, and they get destroyed in under a minute.
Any tips on how I can possible do this map? The computer seems to ignore the player cap / vehicle cap limit and sometimes they have no less than 10 of those spider walker vehicles along with Daemon Prince's x3 and the large superpower thing with tons of health.
Upgraded game to 1.20 so hopefully some decent fixes, although was looking over them and Space Marines seem to get nerfed a lot and Chaos got a boost, so probably even harder 
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, only way i could find of doing it was to rush out with your honour guard and destroy atleast two of the bases.