The WWII U-boats had hulls that resembled surface ships for efficient surface running and the top decks had a lot of drag increasing stuff sticking out, guns, towers, etc.
Modern subs look like topedos and are designed to be efficient under water. Wave generation is a major form of drag on surface boats, especially when they approach or exceed “hull speed”. Hull speed is the speed of a water wave that has the same length as the boats hull. Go above that speed and the water that the hull parted does not have a chance to close again and return the energy needed to part the water back to the hull.
When submerged, the subs don’t generate an energy robbing wake.
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That’s true. The more of the sub that can be raised above the surface of the water while it’s moving is the less resistance the sub will have to overcome. The principle is the same as is used by the racing boat that BLE posted the picture of.
It’s an easy concept to demonstrate. Wave your open (fingers adjacent) hand through the air. Now do the same through water. You’ll discover that the energy difference required is very different. The density of the fluid (air and water are both fluids) is a major factor in energy need (fuel used).
Never said they couldn’t. Snorkels (fitted near the end of the war) had mixed success. From Wiki article on “Submarine snorkel”:
A U-boat with a snorkel raised was limited to six knots to avoid breaking the tube, and its sound-detection gear was useless with the diesel engine running.
Never had any Fast and Furious when I was a youngin, just Roy Rogers and Nellie Bell. Even so it would have been hard to drive too fast in a Morris Minor or VW bug with 36 horses. Only time I ever got stopped was for an open can of Coca Cola.
You could go fast. It would just take you several minutes to get there. 
I would suggest that there’s ZERO doubt that the “ricer” crowd would be mimicking what they’re seeing in the movie. I don’t know if it’s really “confirm able” or not but common sense would suggest that they’re going to hot rod around after seeing it in the movie. My guess is that there was a surge in sales of the Mustang that Steve McQueen drove in the movie “Bullet”. And, I’m s sure, people pushed the cars to the limit to see if it was as fast as in the movie. This isn’t a new thing. People WILL emulate what they see in movies, stupid or not.
Yeah good point. I noticed in the 50’s a lot of people emulating Andy Griffith, Danny Thomas, and Red Skelton. Then there was always Thunder Road for the moon shiners. So there were some fast car shows but all in all I think we can conclude that Hollywood has been a poor influence lately.
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WWII subs used batteries when submerged. They ran on surface at night (or during the day if they had little chance of getting caught) so they could recharge their batteries.
If you’re ever in the Portsmouth NH area - take a tour of the Albacore. It was the first tear-drop US sub. It’s diesel, and was built to test the tear-drop design. It’s a cool tour. I’ve taken the tour a few times. After touring I had a lot more respect for the men that served on subs.
I spent 4 nights aboard an LST in a cot 3 floors below the water line with one cot below me and 4 above me and for 2 days the ship was passing through a typhoon. I really enjoy the water and even boats but I have no desire to go down into another cramped ship. It takes a special kind of man to stay packed in a tin can under the water for weeks and months and I don’t rate.
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As previously posted the late war diesel engine snorkels were unsuccessful. USS Blueback (SS-581) the last of our diesel electric combat capable submarines to be decommissioned is anchored and on display with tours at the Oregon Museum of Science and Industry (OMSI) in Portland Oregon.
I’m not sure how we got from idiotic “ricer” mobiles to submarines but I can dig it!
I think there were far more trying to emulate Dean Martin, Sammy Davis Jr., Hugh Hefner. 
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Sharknado F & F ! The sharks drive the cars!
‘My pappy said, "Son you’re going to drive me to drinkin’ if you don’t stop driving that hot-rod Lincoln."’
I can swim faster and with less effort submerged than I can on the surface, as long as I can hold my breath. Likewise, Olympic swimmers are disqualified if they swim underwater for more than 15 meters following a turnaround.
BLE, are you trying to say that WWII submarines could travel faster and/or with less fuel underwater than on the surface?
Fuel was a major problem for Germany but when they were submerged during the day, they would run on batteries, not diesel. You can’t run on batteries forever without recharging, then would run on the surface with diesel. So really makes no sense to say they used less fuel under water. Of course they did cause you can’t run engines under water.
Long ago I had a pontoon boat and if it wasn’t able to plane off and lift up so that only a few inches were in the water the top speed was less than 10 mph at 5,000 rpm. Once it lifted up the speed increased to 23 mph+ at 5,000 rpm. And often shifting people around would allow the boat to plane off and once planed off and the speed was up to near 20 people could move around with no significant loss of speed. But there are many obvious examples of drag being significantly greater in the water than in the air.
That could be a matter of swimming technique rather than a simple matter of physics.
Ever watch the swimming events at the Olympics. The swimmers are below water more then they are above water.
Yes, I’ve watched Olympic swimming. They don’t move very much like submarines, so I think there are different physics principles at work for each, until submarines start using long arms to propel themselves rather than a propeller and a rudder.
Not German U-boats but modern subs, especially nuclear powered subs which can run full power without air.
There’s a lot of energy in a boat wake and it’s a major factor in a planing surface vessel. Submerged vessels waste no energy creating a bow wake and it offsets the extra wetted area.
If surface swimming was more energy efficient, dolphins would do it.