The German military
The Treaty of Versailles had been very punitive toward Germany, limiting it to an army of no more than 100,000 men, a navy of only a few dozen ships (and no submarines), and an air force of no more than 100 unarmed search and rescue aircraft. Hitler's rebuilding of the German military, in violation of the Versailles terms, actually began in secret in 1933 but went public in 1935. By then Germany already had a 300,000 man army and over 2,000 war planes, with plans for additional buildup.