2009/06/22

The German submarine force size of 1939

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The German navy (Kriegsmarine) entered WW2 with an insufficient quantity of submarines. The quantity of submarines and their production was too low and did not permit to 'defeat' the British in the Second Battle of the Atlantic. The production program eventually expanded to a huge volume, but the submarines were technically and tactically outdated at that point (1943).

I see sometimes comments that insist the Germans did it wrong and should have invested more in submarines during the late 30's.

Well, more submarines would have been 'better' (from a purely German military point of view) - ceteris paribus. More military power is always better ceteris paribus, so that alone doesn't mean much.
The problem is that such a change does not happen ceteris paribus - it comes at an economical and political price. That's where it becomes interesting.

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Let's check history first.

Germany was limited to a 100,000 man army+ navy till 1933. Submarines and military aircraft were forbidden and surface ship replacements were limited.
German submarine designers kept their know-how, though. They developed submarines for foreign customers, for example Finland.

This changed in autumn 1932 - months before the Nazis began to rule - when a plan for a fleet enlargement till 1938 was developed. This included plans for a submarine fleet.
These plans were modified in early 1933 and became outdated quickly. The plans were visibly meant to build a fleet, not so much to be ready for war at a certain time.


Typ I
The navy later settled on a production plan for the Typ I (basic Atlantic sub) and Typ II (short-legged coastal submarine for Northern and Baltic Sea, possibly to French West coast) that favoured the smaller type in favour of a quick growth.
The development and productions preparations were secret.

Typ II
These early plans treated submarines as an integral part of a balanced navy, and the most likely threat navy was the French one.

The Anglo-German Naval Agreement of 1935 changed the restrictions and allowed an overt submarine program.
The British were economically weakened by the Great Depression just as most other nations and were intent on avoiding arms races.
The German navy calculated that the already planned first 36 submarines would weigh 12,500 t, leaving only 9,550 t for additional boats within the new restrictions.

This influenced the plans for additional submarines; the agreement limited the submarine force size for a while (and the sub fleet size limit could only be reached with a trade-off for other warship categories according to the agreement).

The plans for a longer range submarine were focused at a submarine war against French shipping in the Western Mediterranean Sea at that time - not against the British.

Typ VII
This requirement led to the longer-ranged Typ VII and Typ IX submarine classes that dominated the German navy during WW2.

Typ IX
A balanced German navy could have fought successfully against the French in a 1vs1 war. The Germans could have dominated the Northern Sea with small units, raided with cruisers and even larger surface combatants in the Atlantic and harassed French shipping in the Western Med.
A conflict with Russia would have emphasized the need for a surface fleet even more.
It was only the scenario of a war against the huge Royal Navy that required a focus on submarines.

There was a lot of uncertainty about the lethality of anti-submarine technologies such as Asdic (sonar) and depth charges. The loss of complete invisibility under water (even visually in the clear Mediterranean Sea) justified doubts about the submarine's effectiveness and value in comparison to surface combatants.



The shipyards had to expand their capacities to meet the navy's demands - including training skilled workers (welders, for example). Some import raw materials were seriously scarce.

A war against France couldn't have been decided at sea - both countries shared a land border and both the German Ruhr industrial center and the French Paris industrial center were in bomber range. A war at sea would draw resources, but could merely cost the enemy assets, not force one's will on the opponent. Both powers had enough other borders and were almost impossible to block from overseas trade in a 1vs1 war. The serious effects of the British blockade on Germany during the Great War (WWI) couldn't have been repeated.
It was therefore reasonable to not spend much on naval capability as long as France and/or Russia was the anticipated main enemy.

This changed in 1937/1938 when Hitler finally considered the UK as a possible future opponent (he had still sympathy and admiration for the English 'brother nation' and wasn't eager to get into conflict with the UK and its empire at all).

The Second London Naval Treaty of 1936 was meant to replace an earlier agreement, but Germany was not invited to the negotiations of 1935. A bilateral German-British agreement of summer of 1937 updated the '35 agreement instead. This added about 9,500 ts to the German submarine fleet limit.

The Z-Plan of early 1939 still called for a balanced fleet - to be built till 1944! Hitler had tasked the German military to be war ready till 1940, but only in a limited sense.
The full strength (and capability to take on Britain) was expected for 1944 or later.

Meanwhile, the German foreign policy was in a constant gamble - and its success depended on the perception of it being a reliable partner for agreements. A serious violation of agreements was unacceptable till March 1939 when Hitler violated the Munich agreement and thereby ended the British appeasement policy (because he had proved his unreliability).


The declaration of war by Britain and France in early September 1939 was an accidental and unexpected side-effect of the German invasion of Poland. The navy wasn't ready at all because it hadn't been tasked to be ready by late '39.

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This shows why the submarine fleet was too small to cope with the demands placed on it in 1939-1942 and why this was perfectly normal and no failure.

The political costs of a larger pre-war submarine fleet would have been excessive.

The economic ability to produce much more submarines was not really available till about 1938-1939, and that was an awfully short period for a major peacetime fleet build-up.

The submarine fleet was of limited utility in potential conflicts with France or Russia and of no utility against smaller European powers.


There were even more reasons for why the sub fleet was rather small in 1939-1941:

* The personnel of additional submarine units would have caused additional costs and deprived the economy of some workforce.

* An even faster naval expansion would have placed even greater stress on the training system. The overall personnel (senior NCO and officer) quality would likely have suffered.

* A German-British war very unlikely; a war against both France and Britain could only be won if France fell quickly. The industrial and manpower difference was too large for a long war and the devastating effect of the long WWI was still well-known.
The navy could not contribute significantly to such a quick victory over France, but army and air force could - and deserved priority for this reason.
It would have been pointless to hurt Britain at sea if France won the land war.


It's easy to diagnose a weakness of the German submarine force in 1939-1941. It would have been near impossible to change that before the war, though.

The later course of events was not known in advance. Political and economical restrictions as well as the need to hedge against unhistorical scenarios led to the historical submarine force.

The greatest failure of the 1930's submarine programs was probably that eventual quantity production was no major design criterion. That is a problem that happened often in history and that we're facing today again with our peace-time designs.

S. Ortmann

P.S.: I recommend my German readers the book "Geschichte des deutschen U-Bootbaus" (Eberhard Rössler, Bernhard  und Graefe Verlag, 1996). It was also helpful for this blog post.
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1 comment:

  1. That was a very good post. Ok, first of all the Z-plan was a strange animal because such a fleet would have required too much fuel.
    Secondly, it was a very expensive armament with little utility.

    OK, I'm a proponent of carriers, medium sized surface ships and submarines as the ideal mix of pre-WWII and WWII navies and try to keep as much hindsight as possible out of my POV. Such a mix provides the most intelligence and flexible means for a wide range of sea control and sea denial capabilities with engagements of choice unlike the old line of battle.

    The concept of asymmetry seems to have been lost somehow on German military and political thinking. Is it me or did the German force rather reflect their most admired enemy's armament instead of opting for a different balance.

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