Complex sentence: The AK had between 12,000 and 20,000 armed soldiers, most with only small arms, against a well-equipped German Army of 20,000 SS and regular Army units.
Split into simpler sentences: The AK had between 12,000 and 20,000 soldiers, most equipped with only small arms. They faced a well-equipped German army of 20,000 SS and regular army units.