Enrolment in denominational schools dropped sharply and by 1939 all such schools were disbanded or converted to public facilities.[422] Later Catholic protests included the 22 March 1942 pastoral letter by the German bishops on "The Struggle against Christianity and the Church".[423] About 30 percent of Catholic priests were disciplined by police during the Nazi era.[424][425] A vast security network spied on the activities of clergy and priests were frequently denounced, arrested or sent to concentration camps – many to the dedicated clergy barracks at Dachau.[426] In the areas of Poland annexed in 1939, the Nazis instigated a brutal suppression and systematic dismantling of the Catholic Church.[427][428]