The Surcouf and the problem with cruiser submarines

What was the worst submarine design of the Second World War?

Surcouf is the main choice on practical and operational grounds, with a separate objection to hydrogen-peroxide submarines.

Alex Clarke's personal choice is Surcouf because he considers the cruiser-gun submarine concept operationally impractical. That criticism is explicitly separate from his respect for her crew's service. Some Russian and Japanese boats are also mentioned, although the faults are attributed to their technology rather than their basic designs. Another answer objects to hydrogen-peroxide propulsion. The British K class is excluded because it belongs to the First World War.