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I check the search function and couldn't find a post about this specific POD, so please hold the hate.

What if instead of starting Plan Z in January 1939 Hitler instead opts to expand the Uboat force?
http://en.wikipedia.org/wiki/Plan_Z
Plan Z was a combination of a strong battle fleet capable of challenging the British and a big U-boat fleet for commerce raiding. The plan was initially focused on building large surface ships. If war broke out early in the plan, before the large ships were nearly operational, the large ship building program would be halted. This happened in reality when war started in September 1939. The U-boat production was then given priority and the large ship program was stopped.

In the short time from the introduction of Plan Z on January 27, 1939 up to the beginning of war with the United Kingdom on September 3, 1939 only two of the plan's large ships, H class battleships, were laid down (a third one was only days from receiving its keel). At the time components of the three battlecruisers were in production.

At the beginning of the war the large ships ordered before Plan Z were 1 aircraft carrier, 4 battleships, 3 heavy cruisers and 6 light cruisers which were either ready for action or would be ready in the next months. 1 aircraft carrier, 2 heavy cruisers and 3 light cruisers were in early of stages of construction.

With the outbreak of World War II work on the H class battleships, the battlecruisers and even on some cruisers and the two aircraft carriers laid down before Plan Z was introduced was halted, because these large and expensive construction projects would require too much of war essential materials and the materials were diverted to the construction of U-boats.

As it was the construction of capital ships turned out to be a total waste of resource (materials, dock space, and scarce skilled labor) and ended up delaying the Uboat expansion needlessly.
The added benefits of starting the Uboat expansion in 1939 is that training can be started in peace time for large numbers of crews, more experience gained producing Uboats, which reduces construction times, and the British won't be moved to start expanding their escort forces, as they thought they had enough to handle up to 100k tons of Uboats as it was and the Germans won't be able to manufacture up to 100k by the time September 1st rolls around.

The numbers I'm thinking would be just moving up historical production up a year.

http://uboat.net/technical/shipyards/
Historical numbers:
U-boat production:
1935 (14)
1936 (21)
1937 (1)
1938 (9)
1939 (18)
1940 (50)
1941 (199)
1942 (237)
1943 (284)
1944 (229)
1945 (91)

Total: 1153

So that would mean this in my scenario:
1939: 50
1940: 199
1941: 237
etc.

Here are historical losses:
1939
57 U-boats were capable of going out to sea when the war began in September 1939. When the year ended 9 of them had been lost.

1940
24 boats were lost in 1940. U-31 was actually sunk twice so she appears twice in that number.

1941
35 boats were lost during 1941.

1942
The U-boat fleet lost 86 boats during this year, most of them in the latter half the year. A sign of things to come ...

Losses were pretty low until late 1942-1943, which was the result of the US entering the war and finally closing the Atlantic Gap with patrols AND production finally ramping up enough to properly escort convoys and make good losses.
That was also about the time that there were 100 Uboats on station, which was far too late to make a difference.

Here though the production numbers would mean that in mid-1941 there would be over 300 Uboats in service so would then have 100 Uboats on station, which was Admiral Dönitz's 'magic number'. This would also be before the US enters the war and the convoy system gets good at sinking German subs.


Still even in 1940 the Germans would have a massive increase in Uboats, meaning there would be around 150 Uboats available by July-August for operations in the Atlantic (not including the coastal subs still operating in the North Sea.
That would be a massive increase (50) over OTL, which saw less than 20 Uboats on station at that period:
http://uboat.net/ops/combat_strength.html
That's more than 3x the number that were available to be on station during the period that the convoys were at their weakest and the Germans had broken the convoy codes.
IOTL they lacked the numbers to really intercept all of the convoys they knew were coming (17% of convoys actually engaged in 1940), while here they won't really. There will be plenty of chances to form Wolf Packs, which exponentially increased losses, especially in this period (1st Happy Time).

http://en.wikipedia.org/wiki/Battle...me.27_.28June_1940_.E2.80.93_February_1941.29
'The Happy Time' (June 1940 – February 1941)

The early U-boat operations from the French bases were spectacularly successful. This was the heyday of the great U-boat aces like Günther Prien of U-47, Otto Kretschmer (U-99), Joachim Schepke (U-100), Engelbert Endrass (U-46), Victor Oehrn (U-37) and Heinrich Bleichrodt (U-48). U-boat crews became heroes in Germany. From June until October 1940, over 270 Allied ships were sunk: this period was referred to by U-boat crews as "the Happy Time" ("Die Glückliche Zeit").[26] Churchill would later write: "...the only thing that ever frightened me during the war was the U-boat peril".[27]

The biggest challenge for the U-boats was to find the convoys in the vastness of the ocean. The Germans had a handful of very long-range Focke-Wulf Fw 200 Condor aircraft based at Bordeaux and Stavanger which were used for reconnaissance. The Condor being a converted civilian airliner, this was a stop-gap solution for Fliegerführer Atlantik. Due to ongoing friction between the Luftwaffe and Kriegsmarine, the primary source of convoy sightings was the U-boats themselves. Since a submarine's bridge was very close to the water, their range of visual detection was quite limited. The best source proved to be the codebreakers of B-Dienst.

Instead of attacking the Allied convoys singly, U-boats were directed to work in wolf packs (Rudeln) coordinated by radio. German codebreaking efforts at B-Dienst had succeeded in deciphering the British Naval Cypher No. 3, allowing the Germans to estimate where and when convoys could be expected. The boats spread out into a long patrol line that bisected the path of the Allied convoy routes. Once in position, the crew studied the horizon through binoculars looking for masts or smoke, or used hydrophones to pick up propeller noises. When one boat sighted a convoy, it would report the sighting to U-boat headquarters, shadowing and continuing to report as needed until other boats arrived, typically at night. Instead of being faced by single submarines, the convoy escorts then had to cope with groups of up to half a dozen U-boats attacking simultaneously. The most daring commanders, such as Kretschmer, penetrated the escort screen and attacked from within the columns of merchantmen. The escort vessels, which were too few in number and often lacking in endurance, had no answer to multiple submarines attacking on the surface at night as their ASDIC only worked well against underwater targets. Early British marine radar, working in the metric bands, lacked target discrimination and range. Moreover, corvettes were too slow to catch a surfaced U-boat.

Pack tactics were first used successfully in September and October 1940, to devastating effect in a series of convoy battles. On September 21, convoy HX 72 of 42 merchantmen was attacked by a pack of four U-boats, losing eleven ships sunk and two damaged over two nights. In October, the slow convoy SC 7, with an escort of two sloops and two corvettes, was overwhelmed, losing 59% of its ships. The battle for HX 79 in the following days was in many ways worse for the escorts than for SC 7. The loss of a quarter of the convoy without any loss to the U-boats, despite very strong escort (two destroyers, four corvettes, three trawlers, and a minesweeper), demonstrated the effectiveness of the German tactics against the inadequate British anti-submarine methods. On December 1, seven German and three Italian submarines caught HX 90, sinking 10 ships and damaging three others. The success of pack tactics against these convoys encouraged Admiral Dönitz to adopt the wolf pack as his primary tactic.

Nor were the U-boats the only threat. Following some early experience in support of the war at sea during Operation Weserübung, Fliegerführer Atlantik contributed small numbers of aircraft to the Battle of the Atlantic from 1940 onwards. These were primarily Fw 200s and (later) Junkers Ju 290s, used for long-range reconnaissance. The Condors also bombed convoys beyond land-based fighter cover and thus defenceless. Initially, the Condors were very successful, claiming 365,000 tons of shipping in early 1941. These aircraft were few in number, however, and directly under Luftwaffe control; in addition, the pilots had little specialized training for anti-shipping warfare, limiting their effectiveness.

Allied tonnage sunk by U-boats
Year Tons sunk
1939 0,6 million
1940 2,3 million
1941 2,2 million
1942 5,8 million
1943 2,3 million
1944 0,6 million
1945 0,2 million
14 million Total

Seeing as how vulnerable British shipping was in 1940 after the Fall of France, I think it is generous to assume that with more than three times more Uboats on station that losses would tripled, as the primary reason the Uboats IOTL didn't inflict even more losses was the lack of numbers.

I figure the following for shipping losses to Uboats alone:
1939: 1.2 million
1940: 6 million
1941: 6 million
1942: 10 million
1943: 5 million

With numbers like these at what point do Allied operations become badly effected and the British drop out of the war? Remember too that shipping losses were actually higher than this because of losses to mines, aircraft, surface warships, etc.
http://www.usmm.org/wsa/shiploss.html
IOTL over 22 million tons of shipping were lost up to 1943, with 13.2 million caused by Uboats. Here Uboats cause 28.2 million tons of losses, while the remainder, 9.8 million, as all other causes. That's 38 million tons of shipping, which was the total launched by the US from 1939-1945.

Also what about butterflies? If the Uboats increase pressure on the British so much, perhaps the Bismarck slips through into the Atlantic because the British lack enough warships to pursue her.
What are your thoughts?
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