Before revision: The Soviet Union was the first country to officially distinguish this third level of military thinking, when it was introduced as part of the deep operation military theory that its armed forces developed during the 1920s and 1930s .
After revision: and utilized during the Second World WarThe Soviet Union was the first country to officially distinguish this third level of military thinking, when it was introduced as part of the deep operation military theory that its armed forces developed during the 1920s and 1930s .