Although the prewar doctrines of both armies stressed the importance of fortifications, the situation at the border in June 1941 was that many of the fortifications on both sides were incomplete and half-finished. Material and labor shortages as well as the very short interval of time between the Polish campaign and Barbarossa prevented either side from constructing massive fortified areas. This does not mean that either side neglected the issue of fortifications as the Soviets, and to a lesser extent, Germany, had plans for expanding or replacing the prewar network of fortifications that they maintained on the Polish frontier.

In the case of Germany, one of the serious concerns of the German general staff (OKW) was that Stalin would take advantage of Germany's preoccupation with France to attack into Poland. Although Germany maintained an Ostwall of interconnected fortified zones on the former Polish border, the occupation of Poland had rendered these fortifications moot. In a disturbing harbinger of the Holocaust, the SS offered to use Polish Jews, who were now deported en masse to the General Government, as an expendable labor force to construct a new series of lines inside the General Government opposite the USSR's portion of Poland. However, the Fall of France had forced the Germans to reevaluate the needs for a mass of fortifications in Poland. For his part, Hitler had already been entertaining doubts about the efficacy of fortifications. His prewar tours of the Ostwall also led him to disparage the quality of the bunkers. Moreover, victory over France had vindicated Heer leaders' prioritization of the attack and mobility. OKH chief Halder noted in his war diary in June 1940 that "whatever one has must be used for attack," and that German troops detailed for fortifications in Poland must be kept to a minimum and fortifications should focus upon delaying the enemy. The failure of the SS's "Jewish Wall" to accomplish much in the way of actual construction also underscored the need of the Germans not to rely upon fortifications. So on the German side of the border, there were some bunkers, minefields, and tank traps, but nothing terribly substantial. The post-1940 mood within both OKW and OKH was that the USSR was a prime target and constructing any massive fortifications would be rendered irrelevant by a swift occupation of the USSR.

Unlike the Germans, the Soviets tended to place more stock into the power of fortifications. Soviet doctrine tended to favor using fortifications in strategic areas to create a bottleneck or bulwark for mobile forces. Starting in 1928 and continuing intermittently in the 1930s, the Soviets had constructed the Stalin Line along their Western border. Although not a contiguous line of fortifications, the Stalin Line had fortified the Western Military District in the Ukraine and the Baltics at considerable expense. The Soviets though faced the same dilemma as the Germans as the Molotov-Ribbentrop Pact had expanded the borders well past existing fortifications. The Soviets began to construct a new fortified system to match the new border. Known postwar as the Molotov Line, it was a series of interlocking fortified zones that would provide a bulwark against any German invasion and allow for a Red Army counterattack.

The problem for the Soviets was that there were shortages of equipment and labor to fully realize the Molotov Line's potential. The harsh winter of 1939/40 prevented construction and the typically wet springs of Eastern Europe also created delays. The Soviets themselves were also divided over to the actual placement of the new defenses. A number of the Red Army's generals favored locating the new defensive network at some distance from the frontier as they could be observed by the Germans and easily overrun. Stalin though overruled these concerns and instead insisted upon locating the Molotov Line on the frontier. The need to complete this new line quickly meant that the Soviets stripped the Stalin Line of its equipment and it was undermanned.

The Soviet fortification decisions in 1939-41 were really the worst of both worlds and aided the German invasion. As zhukov and Timoshenko feared in the debate on the Molotov Line's placement, the Germans were able to swiftly overrun or bypass the frontier fortifications. Their incompleteness meant that although they were able in spots to take a toll on the German attackers, they could not stymie the German advance in a significant way. The fact that the Molotov Line had used up so much concrete and other resources meant that the Soviets were never able to complete their planned expansion of their network of airfields. The result was the existing airbases were crammed with Soviet aircraft, which made a prime target for the Luftwaffe. Denuding the Stalin Line of its equipment also meant that it was not a significant obstacle for the Germans. Although these fortifications were more complete than the Molotov Line, they were undermanned and under-equipped. As with the Molotov Line. Although the Stalin Line was able in spots to inflict losses on the Germans, most notably with the 3rd SS Panzer Division Totenkopf in Army Group North had to be pulled off the line from losses trying to penetrate the Soviet defenses, the Stalin Line failed to significantly halt the German advance. German air superiority and artillery fire was able to neutralize the Stalin Line and German forces were able to bypass or destroy its fortifications. The poor state of the Stalin Line was noted by a number of German officers, such as Lieutenant-General H.J. von Hoffgarten who noted:

Contrary to the expectations of our units, the Stalin Line did not prove to be the strongest obstacle against our advance. Certainly there were some bunkers and wire obstacles, but they were far less effective than those which I experienced during the breakthrough of the Maginot Line at Sedan on 13 May 1940.

Although some commentators, most notably the Soviet defector Viktor Suvorov, concluded that the cannibalization of the Stalin Line was part of a larger nefarious plot to invade Germany, the reality is the Soviets never fully abandoned the Stalin Line and a number of Red Army commanders recognized the weaknesses of the Molotov Line. As often with military planning, the most important resource is time and this was in short supply in the brief period between 1939-1941.

Sources

Müller, Rolf-Dieter, and Alexander Starritt. Enemy in the East: Hitler's secret plans to invade the Soviet Union. London: I. B. Tauris, 2015.

Short, Neil. The Stalin and Molotov Lines: Soviet Western Defences, 1928-41. Oxford: Osprey Publishing, 2008.

_. Germany's East Wall in World War II. London: Osprey Publishing, 2015.