s class opinion

[LukeFF]

The whole thing about the S boat's submerged speed is that by the time the US entered the war, most of the boats could only make 9-9.5 knots submerged, which was about the same as a fleet boat. Time was not kind to the S class. Frankly, sailors hated serving on these things. Almost every patrol reported noted that the living conditions were poor. If it wasn't the moldy mattresses from all the condensation inside the boat, it was the freezing cold temperatures endured on Alaskan patrols. If it wasn't that, it was the unbearably hot conditions in the South Pacific. If all that didn't get to you, you still had to worry about the batteries exploding due to (again) all that condensation.

All told, an S boat sailor's best day was the day he was transferred off the boat.

[Hitman]

The S-Boat was the first submarine to be optimized for underwater performance, beating the Type XXI U-Boat by 24 years! Smaller and with less power than the later fleet boats, it was faster and quicker handling underwater.

Actually, by WW1 most navies had submarines optimized for underwater performance while not -as you correctly state- for constant underwater operation. Most early submarine designs, including WW1 ones are clearly fish inspired, even with finns, because there was still not a good understanding of underwater dynamics and of the best shape to be used.

In fact, the innovative part of german design in WW1 was to give precedence to submarines as commerce raiders and improve their surfaced sea-keeping abilities with the double hull, reaching the u-cruiser concept as peak, and leaving the underwater performance as something secondary.

[Rockin Robbins]

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.