From the very basic early submarines such as the Type II through to the ultra-modern high tech Type XXI and Type XXIII vessels, German U-Boat production was forced into continual development and improvement to keep pace with wartime needs and especially that of continually having to face ever more effective enemy anti-submarine developments. However, it would not simply the submarines themselves which would need to continuously develop and improve, but the tactics as their prey became increasingly sophisticated in their methods of defence. U-boats were used for a variety of purposes, from coas.