No the problem was the guy they got to run the programme manufactured cars.
So who exactly do you expect to run this 1936 outsourcing programme? After all, the shipbuilders are going to have exactly the same objections to it as they do in 1944, which means bringing in an outside expert. You may not have noticed the irony that, while you decry the ability of a car manufacturer to build U-boats, the people who are managing your inland supply chain probably aren't even going to have experience of manufacturing anything as complicated as a car. That is, unless you propose to take manufacturing capacity away from the army (more capacity, rather, since the German economy is already dramatically over-committed by the late 1930s).
Training is not the issue people make it out to be. In the last 5 years before the war the Germans train millions of troops for Army and Luftwaffe.
And you'll note the vast number of clandestine ways in which the skills required are maintained during the 1920s and 1930s (glider clubs, "gymnastics societies", the Stahlhelm, the SA, the Treaty of Rapallo). You can take commercial pilots or veteran infantry soldiers and have them pass on their skills: there aren't any commercial submarines, and dragging the few remaining World War One veterans out of retirement makes about as much sense as getting A7V veterans to train Panzer crews.
The KM had a more modest programme transition from 15k to 75k. When the war began the navy quickly doubled its size to 150k.
But these are overwhelmingly surface ships, not submarines. The German Navy has been operating surface ships throughout the 1920s and 1930s, so has a pool of reservists with experience to draw on to leaven the new crews with. This explanation even ignores the plain fact that it's far easier to take a helmsman from a commercial cargo ship and turn them into a destroyer helmsman than a member of a submarine crew.
To put things in perspective for you, here's the actual number of new U-boats added to the fleet annually:
1935: 14
1936: 21
1937: 1
1938: 9
1939: 18
1940: 50
Perhaps you'd like to suggest an alternative annual building programme, calculate the percentage increases required over the historical one, then explain again that this won't entail any decrease whatsoever in the quality of crews, let alone the quality of boats, which are churned out.
Top u-boat commanders (as well as their British and American counterparts) were top notch for only a quite short period.
So now let's imagine Prien's sortie against Royal Oak. He's still got the same defences to face, and he's still got the same innate ability. However, this time he's got a helmsman with just over two weeks training, a leading engineer who learned his trade on the Emden's steam turbines and a torpedo team who haven't fired a live round together because production isn't sufficient to allow for training. His bosun and executive officer were promoted a few days before setting sail, to fill gaps in other U-boat rosters. Because the hull sections were manufactured in a factory that formerly specialised in corrugated iron sheeting and welded together in a shipyard that was running behind, the entire boat leaks as soon as it goes below ten metres and is so hydrodynamically mis-shapen that it can't reach over five knots when submerged.
I've argued this sort of thing before, and I can already see the same sort of knee-jerk Third Reich-fanboyism creeping into the discussion. Never mind the fact that U-boat batteries require the very raw materials- copper, rubber, lead- which Germany is running out of even before 1939. Ignore the fact that Doenitz doesn't even start calling for an all-out effort in submarines until November 1937, and isn't in a position to influence policy until well after the start of the war. Assume that Chamberlain will still be happy to reach an accommodation at Munich with a country which is building a submarine fleet which can only be aimed at attacking Britain. Assume that Roosevelt and the American people will ignore the fact that the Germans are quite clearly planning a repeat of the campaign that brought America into the First World War.