Stalin's 'Great Purge' was in 1936-39. When the Nazis invaded Russia in in June 1941, they scored tremendous victories, because the Red Army lacked competent officers and NCO's. 3 million Red soldiers became POW's and virtually all died in captivity. Another 3 million were lost to combat and disease.
Adding to the list of American Generals and Admirals, there is General Stanley A. McChrystal, who was serving as commander of our forces in Afghanistan. His sin was that members of his staff referred to "Vice President Bite Me" in a bar conversation where a Rolling Stone reporter was present.