Excerpts I selected from Wikipedia’s lengthy and disjointed article on this subject:
Catholic Church and Nazi Germany
A threatening, initially sporadic, persecution of the Catholic Church in Germany followed the Nazi takeover. The Nazis claimed jurisdiction over all collective and social activity, interfering with Catholic schooling, youth groups, workers’ clubs and cultural societies. “By the latter part of the decade of the Thirties”, wrote Phayer, “church officials were well aware that the ultimate aim of Hitler and other Nazis was the total elimination of Catholicism and of the Christian religion. …
Immediately prior to the signing of the Concordat, the Nazis had promulgated the sterilization law—the Law for the Prevention of Hereditarily Diseased Offspring—an offensive policy in the eyes of the Catholic Church. Days later, moves began to dissolve the Catholic Youth League. …
Clergy as well as members of male and female religious orders and lay leaders began to be targeted, leading to thousands of arrests over the ensuing years, often on trumped up charges of currency smuggling or “immorality”. Priests were watched closely and frequently denounced, arrested and sent to concentration camps. From 1940, a dedicated Clergy Barracks had been established at Dachau concentration camp.
Catholic schools were a major battleground in the church struggle.
[The Catholic Church] could not silently accept the general persecution, regimentation or oppression, nor in particular the sterilization law of summer 1933. Over the years until the outbreak of war Catholic resistance stiffened….
An estimated one third of German priests faced some form of reprisal from the Nazi Government and 400 German priests were sent the dedicated Priest Barracks of Dachau Concentration Camp alone.