My history books went from wheelbarrows of worthless reichsmarks in 1929 to fleets of tanks, submarines, and ships in 1939 during what I am told was a worldwide economic depression.
How?
Everything you could possibly want to know about this subject and more is under the FAQ on Nazi Economics. If you still have questions after reading through those 14 posts, feel free to hit me up and I'll do my best to help you but I feel that what can be said about the topic in general terms has already been said in those posts.