Complex sentence: The M10/Achilles turret had an extremely slow manual only turret rotation, but this was not a significant tactical issue when the tank was used in it's "proper" defensive role as it was clearly superior to German Stugs which had no turret rotation.
Split into simpler sentences: The M10/Achilles turret had an extremely slow manual only turret rotation, but this was not a significant tactical limitation when the tank was used in it's "proper" defensive role. In this role it was clearly superior to German Stugs which had no turret rotation.