Where is the largest army base in Germany?

No, to my knowledge, their are no foreign military bases within the US, but we DO have bases in Germany as well as many other countries. However, these other countries are not annexed to the US.

While there are no German military installations in the US, German Luftwaffe and Wehrmarkt do attend training in the US at times. Ft. Sill, the US Army Artillery Training School, trains troops and officers from many countries.