[Rockin Robbins]

The United States could have designed submarines to operate more efficiently underwater. After all, the World War I S-Boats were very good underwater and actually were faster there than the fleet boats by a knot. However, the Navy was very interested in sinking more enemy vessels and very uninterested in features which had no payoff, like underwater speed and extreme depth capability. A submarine underwater at great depth is a harmless thing indeed.

The fleet submarine was designed wrong. It was assumed that subs would travel with the fleet and act as pickets, much in the way destroyers are used. That was lunacy, but it almost accidentally ended up with the best configuration for a diesel/electric submarine: a surface raider that can submerge for short periods of time when absolutely necessary.

There are several reasons why operating on the surface for the vast majority of the time was appropriate for diesel/electric subs.

First, the number of contacts you develop is directly proportional to the number of square miles of ocean surface you can search each day. If you are to remain submerged during search operations you can travel at a speed of about one knot all day. On the surface, traveling at best fuel economy, you would be traveling at 9 knots, a nine times increase in track length. Then your search radius improves, especially with radar. Eugene Fluckey calculated that without accounting for radar, based on high periscope search only he could search about 100 times more ocean area on the surface than he could submerged. That may not result in 100 times more contacts, but can you see that the comparison is just crazy good for the surfaced sub?

Second, a sub has to surface to charge batteries. A sub submerged all day surfaces with low batteries, maybe 25% charge left at best, and then spends the entire night with the lousiest possible fuel economy running the engines wide freakin' open not to propel the sub, but just to recharge the batteries. And the sub is not ready for combat during that procedure, having inadequate charge to attack and evade any contacts developed. The sub is at a critical disadvantage, lacking speed and endurance it may need to survive.

Third, for battling planes situational awareness is your friend. Playing ostrich below the surface, there is no way to detect planes overhead. But they certainly can detect you by wake and by direct vision. You will detect them by dying suddenly without notice. On the surface your radar can develop contacts and analyze their movements with plenty of time to submerge before they can possibly detect you. If you wait until they've passed overhead and are far enough away not to detect you, about five minutes after you submerge, you can just pop right back up to the surface without even checking. Why would that work? Your radar has enough range to detect any plane that could be five miles away when you surface. You already know there are none and are perfectly safe as you have not been submerged long enough to ruin your combat awareness.

Fourth, many battle operations are best conducted on the surface, including deck gun operations, initial nighttime approaches and even torpedo attacks. Being on the surface means your sub is at it most maneuverable and nimble configuration. Often you can shoot torpedoes, turn tail and run away on the surface at 20 knots with no problems at all. If you're underwater and they get on top of you, you are in for a long and dangerous interval of being the hunted, not the hunter.

The submarine is to hunt. Hunting means maximum time on the surface.

U-Boats were the hunted. The Type XXI was designed to operate best in ostrich mode, afraid to poke her head above the surface, which was completely controlled by her enemies. With total domination of air and sea by the Allies, the Germans had no choice but to optimize for the only place they could operate with any safety: underwater. In doing so they surrendered their offensive capabilities, but survival was their goal, not victory. For that the Type XXI was a great design. Well, it might have been a great design because it was never used enough to determine its reliability. It could have been a total dog and they never would have known. My guess is that they would have been sticking their fingers in holes in the dike for the entire first year of operation and only 18 or 24 months into operational use would the Type XXI have begun to show what it was good for.

Superboat it wasn't. It was merely the best thing they could come up with to prolong an inappropriate use of the submarine as a weapon in the Battle of the Atlantic--a battle never winnable by German submarines without control of some ocean surface areas and air superiority in coastal approach zones.

Admiral Daniel Gallery's method of location (snorkels could be located easily by radar), drawing an operational radius and covering that circle until the sub popped up would have worked just as well for a Type XXI as it did for a Type VII. That snorkel would have gone down with a couple of bombs or even a strafing run, reducing the Type XXI to a very limited range. Allied control of sea and air was the end of submarine operations no matter what.

Interestingly, after the war, US Boats were fitted with Guppy I conversions with underwater optimized hull modifications. They achieved higher underwater speeds than the Type XXI with no alterations to batteries or electric motors. Later modifications to Guppy II with higher battery capacity and even more streamlining outperformed the Type XXI in all aspects. These were still trivially modified fleet boats, showing that the fleet boat operated they way it did by carefully chosen design, not because the US Navy was behind the Germans in submarine design capability.