In 1919 the German Army was restricted to 100,000 men by the Treaty of Versailes. In 1940 it overran Norway, Holland, Belgium and France, having defeated Poland in a lightning campaign in 1939. This paper looks at how the German Army was firstly preserved and then developed in the interim years between 1919 and 1935. There was in this period a reorganisation based on a systematic study of the tactical and operational lessons of the First World War.The author of much of the change was General Hans von Seeckt, who was the author of "Führung und Gefecht" (published 1924 and reptinted in the original German by MLRS). On the basis of the changes and the training regimes laid down in the inter-war years the German Army became the most effective army in Europe by 1939. This is an excellent paper and worthy of study.