And that was absolutely the correct decision for all diesel-electric boats. Anything that encouraged skippers to stay submerged for one second longer than they were forced to hurt the submarine's ability to survive and find targets.

An underwater optimized boat would have encouraged the ostriches to run submerged all the time, destroying their situational awareness and leaving them sitting ducks which were unable to develop targets. Especially with plane-borne radar, snorkels were large, conspicuous targets. The operators of the submarine were secure in their own ignorance, while the searching planes had no problem finding and destroying their willfully unaware target.

That is one good reason why the Type XXI would have made no difference to the outcome of the Battle of the Atlantic. For diesel-electric submarines to be successful there must be areas where your forces control the surface of the sea or the air above it. At a bare minimum you must be able to hinder the activities of those who search for you.

A quarterback in American football has no possibility of success unless his offensive line protects him long enough to hand the ball off, pass it or run himself. The German navy had no offensive line. So long as the U-Boat was tethered to the surface in any way it could not succeed, for the enemy could hunt it at his leisure and without prospect of harassment.