What Britain learned from captured Type XXIII submarines

How much use did the Royal Navy get from the captured Type XXIII submarines N35 and N31?

They were used extensively for testing and for comparing German hydrodynamic design with British submarine development.

The Royal Navy used the captured boats for extensive testing and design studies. Their hydrodynamic performance could be compared directly with contemporary British work, making them useful experimental assets even though Britain did not adopt them as an operational class.