What if the Type 21 U-Boats became operational in 1940?

Discussions on alternate history, including events up to 20 years before today. Hosted by Terry Duncan.
Carl Schwamberger
Host - Allied sections
Posts: 7141
Joined: 02 Sep 2006 20:31
Location: USA

Re: What if the Type 21 U-Boats became operational in 1940?

Post by Carl Schwamberger » 28 Dec 2019 04:10

glenn239 wrote:
27 Dec 2019 17:48
Takao wrote:
24 Dec 2019 01:59
Says a lot about how successful these Type XXIIIs will need to be...If the Allies are intentionally sinking 50 merchant vessels. Right there is 75 Type XXIIIs worth of sunken ships.
Does anyone know what the effect on a Mulberry would be if it were torpedoed?
The outer breakwater were the floating 'pontoons'. Some of the torpedoes would have detonated on those. Those were cabled together in a chain, and each with multiple anchors. The next breakwater were the hulks grounded bow to stern. Not much point in a torpedo hitting those. The inner breakwater were large concrete cassons, water filled and grounded. The piers had heads that were set on multiple columns, the pier connection to the beach were pontoons, linked & with multiple anchors.

The Mulberrys were in relatively shallow water. Shallower at low tide. They were also constructed inside the German established mine field. I dont know how long it took to clear that, tho its presence did suggest how far out from the coast the water remained shallow. There were also a lot of complex currents in the Channel, that vary by time of day.

The A Mulbeery was hit by a storm it was not designed for, had the triple breakwaters damaged to the point their efficiency was compromised 20% to 30%, had two of its three piers totally destroyed. It still took in cargo discharge in excess of its designed rate for near two months longer than intended. So yes torpedoes could blow things and damage parts. How many torpedoes would it take to equal the June storm?

glenn239
Member
Posts: 4993
Joined: 29 Apr 2005 01:20
Location: Ontario, Canada

Re: What if the Type 21 U-Boats became operational in 1940?

Post by glenn239 » 28 Dec 2019 15:25

Carl Schwamberger wrote:
28 Dec 2019 04:10
The A Mulbeery was hit by a storm it was not designed for, had the triple breakwaters damaged to the point their efficiency was compromised 20% to 30%, had two of its three piers totally destroyed. It still took in cargo discharge in excess of its designed rate for near two months longer than intended. So yes torpedoes could blow things and damage parts. How many torpedoes would it take to equal the June storm?
Thanks for posting that. Interesting.

User avatar
Takao
Member
Posts: 2932
Joined: 10 Mar 2002 19:27
Location: Reading, Pa

Re: What if the Type 21 U-Boats became operational in 1940?

Post by Takao » 28 Dec 2019 20:50

JAG13 wrote:
27 Dec 2019 23:15

Read it, it made a PARTIAL detail of losses, so?

Depth charge attack doesnt mean a sonar contact, something quite hard against such a target in coastal waters...

You only need to swamp the defenses with a large number of attackers, no need to coordinate in detail.

At least you are no longer calling the Type VII a coastal submarine...
While some were lost to weather, poor navigation could also be due to weather...Who is to say.

What kind of sonar contact? Active or passive?

A modicum of communications is needed, or else the mass attack comes off in dribs and drabs, thus it will never swamp the defenses, and will be defeated in detail.

User avatar
Takao
Member
Posts: 2932
Joined: 10 Mar 2002 19:27
Location: Reading, Pa

Re: What if the Type 21 U-Boats became operational in 1940?

Post by Takao » 28 Dec 2019 21:01

JAG13 wrote:
25 Dec 2019 16:47
Richard Anderson wrote:
24 Dec 2019 21:39
glenn239 wrote:
24 Dec 2019 17:00
Takao wrote:
24 Dec 2019 13:19
The Type XXIII, for all it's benefits, is an overpriced way of delivering two torpedoes to a target. The Seehund, for example, was a much cheaper option.
I'm not following why it was one or the other? The Germans were building both.
That's okay, I'm still not clear on how 1944 technology gets transferred to 1940? Time machine? :lol: Or how single examples of the Typ XXI and XXIII completed in June 1944 and barely operational in 1945 could effect D-Day?
Some solutions could have been available with a bit more foresight in 1940, others were borne out of the war and thus unavailable.
Crystal ball foresight.

The snort was invented by the British in WW1, but didn't catch on, the Italians had their own in the late 20s, but it didn't catch on either, and then the Dutch right before WW2. Boats are rather noisy when snorting, and passive sonar is blanked out, not to mention that the exhaust plume is visible for some miles, and the technology was not there to stop the engines if the snort dunked. Not to mention that the threat from aircraft and radar simply was not there in 1940.

Streamlineing was availible, but guns were still seen as necessary. Not to mention that high surface speed was seen as more of a necessity than underwater speed.

More batteries and bigger engines were possible, but that meant larger, less maneuverable boats.

User avatar
T. A. Gardner
Member
Posts: 1954
Joined: 02 Feb 2006 00:23
Location: Arizona

Re: What if the Type 21 U-Boats became operational in 1940?

Post by T. A. Gardner » 28 Dec 2019 21:21

Here's what I see:

Even if built earlier, it is far too limited a weapon system. It's range and crew arrangements limit it to operations in the Channel from maybe Lowestoft to the Isle of Wight. At worst, they along with the Luftwaffe end British coastal convoys in the area (as happened in late 1940 to about late 1941) and are left with no targets.
At best, they create some short term success against these convoys and are then countered by systems designed more or less specifically to take care of them.

No weapon system, particularly a successful one, will go uncountered.

So, outside a very limited, and specific area of operations, the XXVIIB Seehund is completely worthless as a weapon system.

User avatar
Takao
Member
Posts: 2932
Joined: 10 Mar 2002 19:27
Location: Reading, Pa

Re: What if the Type 21 U-Boats became operational in 1940?

Post by Takao » 29 Dec 2019 01:55

I've only ever imagined it as an anti-invasion weapon system.

User avatar
JAG13
Member
Posts: 689
Joined: 23 Mar 2013 01:50

Re: What if the Type 21 U-Boats became operational in 1940?

Post by JAG13 » 29 Dec 2019 02:11

Takao wrote:
28 Dec 2019 20:50
JAG13 wrote:
27 Dec 2019 23:15

Read it, it made a PARTIAL detail of losses, so?

Depth charge attack doesnt mean a sonar contact, something quite hard against such a target in coastal waters...

You only need to swamp the defenses with a large number of attackers, no need to coordinate in detail.

At least you are no longer calling the Type VII a coastal submarine...
While some were lost to weather, poor navigation could also be due to weather...Who is to say.

What kind of sonar contact? Active or passive?

A modicum of communications is needed, or else the mass attack comes off in dribs and drabs, thus it will never swamp the defenses, and will be defeated in detail.
Bad weather certainly complicates navigation.

AFAIK allied passive sonar wasnt very good, the Seehund made very little noise and coastal waters are quite noisy. Active gets a very small targt to work with and seabed reflections further complicate the picture.

Modicum, but a far cry from the usual wolf pack tactics, otherwise and that close to allied DF stations it would be utterly counterproductive.

User avatar
JAG13
Member
Posts: 689
Joined: 23 Mar 2013 01:50

Re: What if the Type 21 U-Boats became operational in 1940?

Post by JAG13 » 29 Dec 2019 02:24

Takao wrote:
28 Dec 2019 21:01
JAG13 wrote:
25 Dec 2019 16:47

Some solutions could have been available with a bit more foresight in 1940, others were borne out of the war and thus unavailable.
Crystal ball foresight.

The snort was invented by the British in WW1, but didn't catch on, the Italians had their own in the late 20s, but it didn't catch on either, and then the Dutch right before WW2. Boats are rather noisy when snorting, and passive sonar is blanked out, not to mention that the exhaust plume is visible for some miles, and the technology was not there to stop the engines if the snort dunked. Not to mention that the threat from aircraft and radar simply was not there in 1940.
I wasnt thinking of snorkels nor aircraft yet, far too much for the Germans that early IMHO, the need for ESM on the other hand should have been obvious since the KM was operating ship-borne radar since early 1938 adn even were concerned about using it and broadcasting their presence.
Streamlineing was availible, but guns were still seen as necessary. Not to mention that high surface speed was seen as more of a necessity than underwater speed.

More batteries and bigger engines were possible, but that meant larger, less maneuverable boats.
But radar kills surface mobility anyways, certainly surface attack once you need to consider the eventual inevitability of enemy radar equipped-escorts, so you either give up subs or adapt by going true submarine... or you play German ostrich and pretend radar doesnt exist like Dönitz did, of course.

What he actually did sounds more like a bad movie plot.

Return to “What if”