A high underwater speed Type IX

Discussions on alternate history, including events up to 20 years before today. Hosted by Terry Duncan.
User avatar
T. A. Gardner
Member
Posts: 2423
Joined: 02 Feb 2006 00:23
Location: Arizona

A high underwater speed Type IX

Post by T. A. Gardner » 15 May 2021 05:31

I think the Germans made a grave error in waiting for the Type XXI to get into production while doing little to upgrade their existing U-boat designs. What I am suggesting here is that they decide to upgrade the Type IX as an intermediate, or even stopgap, design until they can get the Type XXI in production. This idea follows what the USN and RN did postwar with existing submarines to convert them into high underwater speed boats.

In this scenario, the Germans in say early 1943 design into the Type IX modifications that would produce a higher underwater speed without truly major changes to the boat. These would include:

Removing the deck gun, magazine for it, and other top hamper that induces drag underwater.
The conning tower is redesigned to streamline it.
The deck casting and free flooding vents are redesigned to eliminate parasitic drag on the boat.
As practical, new sections are added into the boat making it slightly longer but giving a big increase in the battery capacity.
New larger electric motors are installed to drive the boat at higher speed.
The snorkel is retained, of course.

Let's say for sake of argument, that the whole of this provides a speed of 12 knots for say 30 minutes submerged, and a 8 versus 6 knot speed for several hours. The boat could also run at 8 to 10 knots continuously with bursts to 12 while snorkeling. This means the boat can now make submerged transits nearly twice as fast as they did before decreasing both the chances of detection and being sunk in transit to and from operational areas.

12 knots is sufficient to render a Flower class corvette worthless as an ASW platform versus such a boat. It would make attacking and sinking this boat much harder for any other platform.
The Germans already have the GHG in service for sonar so they have a great set for operating underwater already in use.

The whole would significantly improve the Type IX in 1943 when it was starting to face seriously dangerous levels of Allied ASW platforms.

EwenS
Member
Posts: 173
Joined: 04 May 2020 11:37
Location: Scotland

Re: A high underwater speed Type IX

Post by EwenS » 15 May 2021 08:56

I found this article on RN tests against HMS Seraph which had been converted as an unarmed high speed targeting mid 1944 as a result of the threat of the Type XXI which may offer some clues.
http://rnsubs.co.uk/articles/developmen ... rettyPhoto

A few points.
1. You would also need to change the propellers on your modified Type IX to reduce cavitation. See the end of the Seraph article.
2. German Snorkel trials only began in summer 1943. By D-Day only about half the fleet had been refitted. So surely your modified Type IX won’t be available until 1944.
3. I’m not sure how much you would gain in transit times. In 1943 U-boat tactics were still for surface transits. They are not going to be running at high underwater transit speeds on batteries as that bigger battery then takes longer to recharge. Even a Type XXI batteries were more quickly recharged on the surface. Snorkelling at high speed increases the wake from the snorkel head making it more visible to aircraft. In 1945 the Mark 1 eyeball seems to still have been the best way for an aircraft to detect such a sub. Also generates a bigger exhaust plume which in colder conditions is easily spotable. Again in winter 1944/45 that was a prime way of spotting these boats.
4. Allied airborne ASW tactics in 1943/44 in the Biscay area relied on ensuring aircraft passed over an area every hour or so to keep U-boats down. Surely that is going to be equally effective against your boat? Faster transit burns battery more quickly forcing snorkelling or surfacing.
5. The Allies were very quickly able to change tactics to fit a new threat and did so. Again see the Seraph article.

EwenS
Member
Posts: 173
Joined: 04 May 2020 11:37
Location: Scotland

Re: A high underwater speed Type IX

Post by EwenS » 15 May 2021 18:39

Here are a few relevant dates and time periods.

Early 1943 - decision taken to design & build the Type XXI (before that it was the hydrogen peroxide sub that was being favoured as the enxt step in U-boat design).
Aug 1943 - Snorkel tests on Type IIC U58
6 Nov 1943 - Type XXI orders placed.
March 1944 - First Type XXI laid down.
June 1944 - First Type XXI completed.

The length of time needed to build a Type IXD/42 U-boat in the traditional way is about 12 months.
The work up period for the final Type IX boats completing in Mar/April 1944 is about 10 months. Even in 1942 that was taking about 7 months.

So take your idea and begin the design in early 1943. How long to redesign and issue new plans to builders? Then a year to build it plus 10 months to work it up. I'm not seeing any operational product much before spring 1945.

By then the U-boat bases in France have been closed. And the Allies have already worked out techniques to tackle your fast U-boat. Also by that time the U-boat war has moved into British inshore waters where the Type IX (let alone a lengthened one) is not the ideal sub. Then we have the issue of disruption in the traditional shipyards from Allied bombing which the prefabricated Type XXI was designed to avoid (OK it brought other problems).

So where is the benefit?

rcocean
Member
Posts: 492
Joined: 30 Mar 2008 00:48

Re: A high underwater speed Type IX

Post by rcocean » 15 May 2021 20:09

Allied airborne ASW tactics in 1943/44 in the Biscay area relied on ensuring aircraft passed over an area every hour or so to keep U-boats down. Surely that is going to be equally effective against your boat? Faster transit burns battery more quickly forcing snorkelling or surfacing.
Even in the best conditions, a Snorkeling U-boat had 1/3 the Radar Footprint of a surfaced U boat. The rougher the seas and the bigger the waves, the smaller the footprint got. Plus it was extremely difficult to attack a snorkeling U-boat at night, since you had to SEE the Snorkel to accurately place your depth charges. OTOH, I assume FIDO would be effective against noisy subs using their diesels.

maltesefalcon
Member
Posts: 2016
Joined: 03 Sep 2003 18:15
Location: Canada

Re: A high underwater speed Type IX

Post by maltesefalcon » 16 May 2021 01:07

U-boats could only carry so many torpedoes. Therefore they relied fairly heavily on their deck armament for attacking at night while surfaced and for the odd unarmed freighter or lower value target that was not sailing in convoy.

Instead of omitting the deck gun, I'm wondering if there was a way to put it on a retractable mount of some sort and have doors that would fair it over to streamline it during submerged transit.

User avatar
T. A. Gardner
Member
Posts: 2423
Joined: 02 Feb 2006 00:23
Location: Arizona

Re: A high underwater speed Type IX

Post by T. A. Gardner » 16 May 2021 06:35

EwenS wrote:
15 May 2021 08:56
I found this article on RN tests against HMS Seraph which had been converted as an unarmed high speed targeting mid 1944 as a result of the threat of the Type XXI which may offer some clues.
http://rnsubs.co.uk/articles/developmen ... rettyPhoto

A few points.
1. You would also need to change the propellers on your modified Type IX to reduce cavitation. See the end of the Seraph article.
Not a major problem. That could have been done easily
2. German Snorkel trials only began in summer 1943. By D-Day only about half the fleet had been refitted. So surely your modified Type IX won’t be available until 1944.
Give priority to the upgraded boats so by the end of 43 they're the ones with a snorkel.
3. I’m not sure how much you would gain in transit times. In 1943 U-boat tactics were still for surface transits. They are not going to be running at high underwater transit speeds on batteries as that bigger battery then takes longer to recharge. Even a Type XXI batteries were more quickly recharged on the surface. Snorkelling at high speed increases the wake from the snorkel head making it more visible to aircraft. In 1945 the Mark 1 eyeball seems to still have been the best way for an aircraft to detect such a sub. Also generates a bigger exhaust plume which in colder conditions is easily spotable. Again in winter 1944/45 that was a prime way of spotting these boats.
It would be substantial. First, a snorkel equipped boat can run underwater indefinitely--well, to the limit of fuel aboard. This means the battery stays charged while snorkeling. If the boat has ESM on the snorkel, as U-boats often did, the boat can detect an Allied search radar and stop snorkeling and run on the battery at higher speed for say an hour or so, then resume snorkeling if the ESM shows clear.
IR in the WW 2 period was sufficiently indiscriminate and short-ranged that this method of detection is not available or practical. A steady running diesel engine doesn't puff out much, if any, visible smoke.
Thus, in a sea with small white caps on it, spotting a snorkeling submarine running on diesel is going to be tough.

Image

That would be enough to make a snorkel difficult to detect in daytime. At night it would be impossible.

4. Allied airborne ASW tactics in 1943/44 in the Biscay area relied on ensuring aircraft passed over an area every hour or so to keep U-boats down. Surely that is going to be equally effective against your boat? Faster transit burns battery more quickly forcing snorkelling or surfacing.
So the boat stays submerged running on its diesels at say 10 knots. That's easily double the transit speed of a submerged un-upgraded Type IX.
5. The Allies were very quickly able to change tactics to fit a new threat and did so. Again see the Seraph article.
You need to re-read that article. The Allies discovered numerous issues and difficulties they'd face versus a faster submarine. That isn't to say the Germans would have it all their way, but rather to say that a faster boat makes a much harder to kill target.

User avatar
TheMarcksPlan
Member
Posts: 2132
Joined: 15 Jan 2019 22:32
Location: USA

Re: A high underwater speed Type IX

Post by TheMarcksPlan » 16 May 2021 06:58

EwenS wrote:I found this article on RN tests against HMS Seraph
The article has basically zero worth as analytical work addressing Type XXI threat (its explicit purpose) and dubious worth re a 12kn sub (the thread topic). It points to the possibility of maintaining contact with a 12kn but doesn't move from that subset of the tactical problem to reviewing the larger strategic picture of BoA and attritional warfare.

What would a semi-intelligent move from tactical to strategic look like? On the narrow tactical issue of maintaining contact, failure there means failure to kill the sub. The strategic attritional equation is directly related to this tactical parameter: 1/3 the kill rate per contact means 3x the rate of attritional success by the U-Boats. From the article's narrative, guessing 1/3 the kill rate seems optimistic.

3x the attritional success for the U-Boat Waffe would certainly have changed the strategic picture in WW2, probably nixing Overlord and/or Husky and/or Pacific campaigns due to shipping shortage.

...and that's looking only at the narrow tactical issue of ASW kill rate per contact.

Other tactical factors include (1) Sub's ability to convert contact into attack and (2) sub's ability to convert attacks into kills.

(1) varies with the sub's ability to evade escorts and get into a firing position. T21's ability to do so would be vastly greater than T7/9, as it had submerged tactical sprint ability that T/7/9 lacked. Let's say 3x as successful for T21 vs. T7/9.

(2) varies with the number of torpedoes fired per attack and the effectiveness of those fish. T21 could fire 3x the torpedoes as T7/9 in 20 min.

Taking together the foregoing tactical parameters and their posited deltas (T21 vs. T7/9), we get T21 having at least 27x the attritional ratio in convoy battles (this doesn't incorporate other tactical issues like pre-convoy air ASW - there T21 had advantages over schnorkel'd T7/9 but not as great).

---------------------

Given the article's failure to relate the tactical and strategic and its non-analytical, credulous praise of the Allies for even trying to counter fast subs (a 1940's "effort trophy"), I'm not inclined to credit its "analysis" of ASW vs. a 12kn sub.

----------------------

I've cited a much more sophisticated work on the Seraph trials in another thread.

As discussed in that thread, even in 1948-9, RN was not optimistic about killing fast subs:
The exercises in 1948–49 with Madden’s 6DF had confirmed that anti-submarine
ships had, as anticipated, a limited capability against a fast submarine. Tactical
procedures were needed, therefore, to take advantage of every fleeting detection.
As for the ships’ systems, while the existing Type 144 Asdic and Squid combination
was reasonably efficient against submarines whose speed was less than 12 knots,
against faster submarines it would only achieve a kill in very favourable
circumstances.
85
https://medium.com/counterfactualww2
"The whole question of whether we win or lose the war depends on the Russians." - FDR, June 1942

User avatar
TheMarcksPlan
Member
Posts: 2132
Joined: 15 Jan 2019 22:32
Location: USA

Re: A high underwater speed Type IX

Post by TheMarcksPlan » 16 May 2021 07:10

EwenS wrote:1. You would also need to change the propellers on your modified Type IX to reduce cavitation. See the end of the Seraph article.
Why exactly? HP and RPM are directly related, RPM is directly related to cavitation. A 12kn T9 is using far less HP and RPM submerged than surfaced so it's not near its cavitation limit.

Cavitation would, of course, increase vs. a 7.3kn submerged speed. But that's a tradeoff between hydrophone and sonar detection and, as the article discusses, high cavitation could mask sonar's effectiveness by blinding it white noise.
EwenS wrote:5. The Allies were very quickly able to change tactics to fit a new threat and did so. Again see the Seraph article.
...and everyone changed tactics in response to the atomic bomb. That adaptation is possible doesn't mean a weapon system is defeated or that it is not dominant. Again, there must be some connection between tactical adaptation that ameliorates a new weapon's dominance and the broader strategic/tactical question of whether the new weapon is dominant despite adaptation. The article fails completely to connect - even to recognize - these issues, as is common with discussion of T21 IMO.
https://medium.com/counterfactualww2
"The whole question of whether we win or lose the war depends on the Russians." - FDR, June 1942

User avatar
TheMarcksPlan
Member
Posts: 2132
Joined: 15 Jan 2019 22:32
Location: USA

Re: A high underwater speed Type IX

Post by TheMarcksPlan » 16 May 2021 07:13

T.A. Gardner wrote:the Germans in say early 1943 design into the Type IX modifications that would produce a higher underwater speed without truly major changes to the boat. These would include:
Whether your proposal is viable comes down to technical parameters that we could analyze with decent accuracy (drag, HP, battery capacity, hull space) if we had decent data and your "blueprints." I could see making an argument for this proposal along the lines you suggest but first why don't you provide some technical parameters and data?
https://medium.com/counterfactualww2
"The whole question of whether we win or lose the war depends on the Russians." - FDR, June 1942

User avatar
TheMarcksPlan
Member
Posts: 2132
Joined: 15 Jan 2019 22:32
Location: USA

Re: A high underwater speed Type IX

Post by TheMarcksPlan » 16 May 2021 07:26

T.A. Gardner wrote:That would be enough to make a snorkel difficult to detect in daytime. At night it would be impossible.
...and that's pretty much exactly what happened OTL. With Schnorkel, Uboats were about as safe at sea as they were in '41. Only problem was that they were useless unless a ship basically ran over them. Late-war T7/9's were akin to self-propelled mines.
T.A. Gardner wrote:Give priority to the upgraded boats so by the end of 43 they're the ones with a snorkel.
Were your proposal adopted, presumably Germany would be pouring more resources into Uboats - as happened later with T21. So I don't think you're bound by OTL Schnorkel output, provided there's a feasible argument that the strategic benefit of faster T9 would outweigh the costs to other armament programs. Given the outsized benefits of the Uboat war to Germany before mid-'43, that's probably an easy argument to make.
https://medium.com/counterfactualww2
"The whole question of whether we win or lose the war depends on the Russians." - FDR, June 1942

thaddeus_c
Member
Posts: 676
Joined: 22 Jan 2014 03:16

Re: A high underwater speed Type IX

Post by thaddeus_c » 16 May 2021 18:10

just IMO, any evolutionary changes would be better than their historical path, which was basically to wait on the new Type XXI, and btw let's try new modular construction also?

like a broken record I'm still stuck on the smaller types though, the KM should have begun with Type XXIII for Elektroboote development, if you want more evolutionary development, return to the Type II (or at least Type II-sized u-boats)

Tom from Cornwall
Member
Posts: 2475
Joined: 01 May 2006 19:52
Location: UK

Re: A high underwater speed Type IX

Post by Tom from Cornwall » 16 May 2021 21:30

T. A. Gardner wrote:
16 May 2021 06:35
It would be substantial. First, a snorkel equipped boat can run underwater indefinitely--well, to the limit of fuel aboard.
Hmmm, why didn’t snorkel equipped U boats stay on the surface indefinitely then? Sunbathing perhaps?

Regards

Tom

User avatar
T. A. Gardner
Member
Posts: 2423
Joined: 02 Feb 2006 00:23
Location: Arizona

Re: A high underwater speed Type IX

Post by T. A. Gardner » 16 May 2021 23:17

Tom from Cornwall wrote:
16 May 2021 21:30
T. A. Gardner wrote:
16 May 2021 06:35
It would be substantial. First, a snorkel equipped boat can run underwater indefinitely--well, to the limit of fuel aboard.
Hmmm, why didn’t snorkel equipped U boats stay on the surface indefinitely then? Sunbathing perhaps?

Regards

Tom
Snorkeling at that time was hard on the crew and nowhere as nearly refined as it is today. Also, if the boat could run on the surface it had a greater range of detecting targets and could cover more ocean at higher speeds, so there were advantages to being surfaced in a submarine designed to operate primarily surfaced. Change that to a design that can run submerged at higher speeds and that changes that dynamic.

User avatar
T. A. Gardner
Member
Posts: 2423
Joined: 02 Feb 2006 00:23
Location: Arizona

Re: A high underwater speed Type IX

Post by T. A. Gardner » 16 May 2021 23:24

TheMarcksPlan wrote:
16 May 2021 07:13
T.A. Gardner wrote:the Germans in say early 1943 design into the Type IX modifications that would produce a higher underwater speed without truly major changes to the boat. These would include:
Whether your proposal is viable comes down to technical parameters that we could analyze with decent accuracy (drag, HP, battery capacity, hull space) if we had decent data and your "blueprints." I could see making an argument for this proposal along the lines you suggest but first why don't you provide some technical parameters and data?
A reasonable starting point would be looking at the Japanese I 201 class submarines. These are about the same size and displacement as a Type IX C U-boat and possess most of the requisite performance levels this redesign would require.

https://upload.wikimedia.org/wikipedia/ ... ns.svg.png

Tom from Cornwall
Member
Posts: 2475
Joined: 01 May 2006 19:52
Location: UK

Re: A high underwater speed Type IX

Post by Tom from Cornwall » 17 May 2021 18:14

TheMarcksPlan wrote:
16 May 2021 06:58
I've cited a much more sophisticated work on the Seraph trials in another thread.

As discussed in that thread, even in 1948-9, RN was not optimistic about killing fast subs:
As usual, someone lauding a piece of work that supports their view on a subject without stopping to consider the intellectual flaws in the trial construction whilst dismissing anything that contradicts their entrenched viewpoint as hopeless. :roll:

Regards

Tom

Return to “What if”