You can fire officers that perform poorly, that isn't a purge; murdering on faked charges a huge part of your officer corps is beyond the pale.
The main problem is that there were a very difficult questions - what to do with the officers left behind and, most importantly, what to do with former military leaders. Demotion was tried - it turned out badly. Tried to lay off for civil service - it turned out badly. I'll explain why.
For example, the pre-war leadership of the Air Force, from 1930 to 1937 did not even bother with the general question "why aviation is needed and how to implement the connection of aviation and ground forces". It was not decided whether we are doing frontline aviation, or strategic one. Instructions were not designed. Just drill trainings and army discipline lessons (the times of
Alksnis).
The only intelligent expert on the combat use of aviation - died in 1938 (Alexander Nikolaevich Lapchinsky), and the rest were... not so good. Appointed from scraps, and they could not cope. Smushkevich was looking bright in the Far East, had real merits, but later showed himself in Khalkhin-Gol: he can not manage aviation (having three times more planes, the USSR in the air above Khalkhin Gol could barely bring air battles to the "draw", having lost more than Japanese, three quarters of the time it was the Japanese who dominated the air).
What the Rychagov did, you probably know. The question of the high accidents at takeoffs and landings of aircrafts was discussed, and as a result it was Rychagov who arbitrarily ordered the flight training to be
stopped, so that the
accident rate would improve. As a result,
two years the air regiment simply were not flying and performing drills, so the accident statistics... was not spoiled. When it was discovered, Rychagov instantly faced huge problems. A genius approach - if you do not fly, then there will be no accidents.
Then problems of a different kind began. The bad performers was just nowhere to attach. The army of wartime has, unlike a peaceful one, plenty of places to send a person unable to command, so that he could be useful at this place (supply, military acceptance of products at the factories etc etc). In the tiny sized army of 1937-1938 there was simply no such "warm places".
Government tried to demote them, to appoint bad performers as merely a divisional commanders instead of executions. It turned out badly.
It turned out that this can not be done - first, we offend those who are honestly going through their careers and intend to take these positions in command INSTEAD of the mistreated "big masters", and secondly, it reduces the overall discipline - the principle of "there is no irreplaceables" ceases to work.
Then government began to change the most odious figures, in the first place the dreamer Tukhachevsky, who for 7 years did not bother with the simple matter of supplying ammunition and fuel for his "deep operations." Then the master of Minsk, Uborevich, who did not have the 'Red Army soldiers' in Belarus SSR, but called them "my own fighters".
Then government came to the Trans-Baikal governor Blucher (who after being reported that the Japanese have already been shelling the border guards for two days, said softly that it was not his business, but the business of NKVD and border guards).
I have here on my table two volumes of
meeting minutes from the annual meetings of the military council at the People's Commissariat of Defense - years 1934 and 1937... Everything is the same - "statistics mistreatment, fraud, distortion of reality, failure to provide a realistic situation" - and still no repressions among the commanders yet. The commanders, whose affairs are dealt with by the commission, they themselves are burning each other - you drank with the Trotskyites, and you started providing prostitutes to the troops, and you ... Really disgusting cowardice, blaming everyone around and begging for a pardon, even there is no talking about executions yet... One of the most reasonable figures there is someone called Stalin I.V -- he moderates the blaming talks and tries to talk these commanders into the reason, while calling for a professional dispute, not the blame-shifting.