Ironically, in the early 1930s until the Spanish War, German officers were conducting secret testing of a new way of employing tanks, infantry and artillery offensively in the Soviet Union with the cooperation of the Red Army. In Germany, these developments eventually culminated in tactics that later came to be known as Blitzkrieg, while in the Soviet Union they formed the core of the deep battle operational doctrine. The successful test of the latter was during the Battles of Khalkhin Gol although the Red Army foundered on the Mannerheim Line in 1940, largely due to the purge in the Officer Corps, claiming many of the senior proponents of the new doctrine. Anti-tank artillery would be included in mobile tank-led Wehrmacht and Red Army units due to the possibility of encountering enemy tanks in a meeting engagement.