The Sudeten Crisis in the summer of 1938 may to some extent have been accountable for the inconsistencies in the handling of the Lake Khasan incident, and the threat of war in Europe it raised undoubtedly precipitated a hasty Soviet withdrawal from direct engagement in the Spanish Civil War. The ‘volunteers’ were all brought home by summer’s end, even though the war itself was not moving rapidly toward a conclusion. Some returned to discover that the Spanish experience and the effects of the purge combined to boost their careers beyond all normal expectations. Others learned that service abroad could be equated with treason. While not as large as those of Italy or Germany, the Soviet participation had been substantial. Some 3,000 Red Army ‘volunteers’ had served with the Republican forces; and the Republic had received (allegedly in exchange for the Spanish gold reserve) in excess of 800 aircraft, 450 tanks and other armored vehicles, 1,500 artillery pieces, 500,000 rifles, 15,000 machine guns, and ammunition and aerial bombs.

Although the intervention in Spain failed, it was taken to have generated a priceless fund of experience. As Isserson put it, the war in Spain ‘opened the curtain somewhat on the battlefield of the future’, an intensely significant concern to all armies and above all to the Red Army. Moreover, to military analysts from many nations, peering over each other’s shoulders, so to speak, it offered a completely consistent picture from start to finish. At no other time during the century had armies possessed so apparently reliable a model from which to work.

In articles published in 1938 in the General Staff ’s new journal, Military Thought, Kombrig S. Lyubarskiy drew a single overarching lesson from the Spanish experience: ‘History repeats itself.’ The defensive superiority that had dominated the World War had reasserted itself more strongly in Spain. Advanced technology had benefited it more than it had the offensive. Deep operations had showed even less promise than in the World War. While the deep operation might well be the only effective offensive form, it would demand ‘enormous strength and the most advanced technological means’; and the war would still ‘assume a prolonged character’.

Lyubarskiy concluded that technology would figure more heavily in battles than ever before, but the infantry mass would ultimately decide wars. Artillery would indisputably retain its place as the most important support weapon, and improvised and permanent fortifications would be essential. The airplane had matured into a powerful offensive and defensive weapon, and the contest for air supremacy over the battlefield would henceforth be a permanent characteristic of warfare.

The tank, in Lyubarskiy’s estimation as also in those of most non-Soviet analysts, had given a distinctly mixed performance. On the offensive, it had provided indispensable moral support for the infantry. In fact, infantry attacks had seldom succeeded without it. On the other had, it had not achieved either ‘large or small successes’ independently of the infantry. The visions of tank formations breaking through prepared positions or even advancing across the open field had not materialized. Moreover, the tanks had frequently experienced ‘great difficulties’ without artillery support; and they had been vulnerable to antitank guns as light as 20mm, which indicated that infantry platoons could probably be armed to defend themselves against tanks.

Kombrig A. N. Lapchinskiy, who held the air tactics chair in the Frunze Academy, completed a book, The Air Army, in 1938, shortly before he was caught up in the purge. As most other commentators on air doctrine also did in the 1930s, he identified three primary air missions: long-range (strategic) bombing to destroy the enemy civilian population’s morale; interdiction bombing directed against the enemy’s communications lines; and close battlefield support. The war in Spain, he concluded, had proved the last to be by far the most significant, because it had demonstrated that ‘only destruction of the enemy armed mass’s will to fight secures victories’. Bombing attacks on cities, such as those on Madrid and Guernica, had neither damaged civilian morale nor impaired the armed mass’s will to fight; hence, bombing civilian targets would not be worthwhile as long as the enemy was holding his own on the battlefront. Interdiction strikes against an adversary’s communications lines would be profitable only if they could be executed without detracting from the effort on the battlefield.