 Red Army deep operations found their first formal expression in the 1929 Field Regulations, and became codified in the 1936 Provisional Field Regulations (PU-36).The Great Purge of 1937–1939 and the Purge of 1940–1942 removed many leading officers from the Red Army, including Tukhachevsky himself and many of his followers, and the doctrine was abandoned.Thus at the Battle of Lake Khasan in 1938 and in the Battle of Khalkhin Gol in 1939 (major border clashes with the Imperial Japanese Army), the doctrine was not used.