It was an invasion worthy of a massive adversary. On November 30, 1939, half a million Soviet soldiers swarmed north, armed with tanks, bombs, machine guns and an astonishing number of troops. The conflict called the Winter War had begun—but the Soviet Union’s enemy wasn’t the war-mongering Third Reich. It was its relatively tiny Baltic Sea neighbor, Finland.

Outgunned, outnumbered, and taken by surprise, it seemed inevitable that Finland would have to concede to Joseph Stalin’s unpopular attempt to assert the Soviet Union’s power in the region. But for a brief moment, an unlikely ally seemed like it might save the day for Russia’s much smaller foe: sausage.

During a short engagement nicknamed the “Sausage War,” Finland struck back. And that momentary reversal in Soviet fortunes influenced more than empty stomachs—it helped convince Hitler that it might be worthwhile to try to invade Russia during the Second World War.

During 1939, as Europe worried about Germany’s warmongering, an armed conflict between the Soviet Union and its neighbor began to seem inevitable. Stalin resented Finland, which had once been Russian territory and which had long fought back against attempts to assimilate it into Russian culture. Though the nation was relatively small compared to the Soviet Union, its loss—sustained during Russia’s chaotic transition to socialism in 1917—represented the diminishment of the once great Russian Empire.

Meanwhile, behind the scenes, the Soviet Union and Nazi Germany secretly agreed not to interfere with one another’s territorial ambitions in certain parts of Europe. Although the Soviet Union and Finland had signed a decade-long non-aggression pact in 1932, Stalin began publicly demanding that Finland cede territory just a few years later. When Hitler invaded Poland in September 1939, the Soviet leader saw his opening to go into Finland.

On November 30, 1939, Soviet forces bombed Helsinki and invaded Finland. The international community was outraged, but Soviet victory seemed inevitable. Given that Soviet forces outnumbered Finnish ones three to one, it looked likely that the war would only last a few weeks.

But though the Soviet invasion had plenty of shock and awe, the forces who headed over the border in November 1939 were in anything but fighting shape. Throughout the 1930s, Stalin had worked to consolidate his power within the Soviet Union by purging the Red Army.Between 1937 and 1939, over 30,000 high-ranking officers were discharged; many were arrested and killed. High-ranking officers were removed, too, with Stalin’s supporters installed in their places.

The purge had dramatic effects on rank-and-file troops in the Red Army. The new officers were less experienced and decision-making now rested largely in the hands of government bureaucrats instead of army officers. This backfired in chilly Finland. Many Red Army troops were from warmer parts of Russia, and the army offered little to no training in winter combat conditions. Meanwhile, the army was unable or unwilling to properly feed its troops—and the Finnish resistance was both better fed and perfectly at home in their icy surroundings.

Despite these challenges—and their empty bellies—the Red Army moved forward. On the night of December 10, a Soviet battalion staged a surprise attack on Finnish troops near the eastern village of Ilomantsi. It should have been a slam-dunk for the Soviets, but by then they were starving. When the battalion came across the Finnish fighters’ cooking tents, they smelled the irresistible scent of sausage stew—fat-heavy rations designed to keep the Finns fighting in freezing conditions.

The food proved too much for the hungry Soviet troops, who paused in their attack to fill up on the Finnish sausage. By then, the Finns had gotten word of the attack. They used the pause to their advantage, surrounding the Russians and staging a surprise of their own.

It was a bloodbath. According to historian William Trotter, the attack was one of the few times bayonet fighting was recorded during the Winter War. “It was close, brutal, and without mercy,” he writes. The ambush—and the gruesome hand-to-hand combat that followed—completely routed the Russian battalion. Only a few men survived.

The “Sausage War,” as it was dubbed, was only a brief battle. But it illustrates both the disorganization of the Red Army and the surprising savvy of the Finns. Still, sausage was not enough to stop the invasion: After 105 days of war, Finland was overwhelmed by the Soviets’ sheer firepower. The country surrendered and ceded territory to the Soviet Union.

The brief, sausage-laden battle was just a momentary blip, but it wasn’t the only instance of fierce Finnish fighting—or Red Army ineptitude—during the Winter War. And someone was paying close attention to dispatches from the battlefield: Adolf Hitler. Thanks to reports of the Red Army’s incompetence, Hitler began to think of the Soviet Union as a target for invasion.

Ironically, Hitler and his officers didn’t learn from the other major takeaway of the Winter War—that a snowy, icy invasion can be nearly impossible to sustain without adequate training, weapons and food. German troops would surely have appreciated some hot sausage during the interminable invasion of Russia in 1941—but the lessons of the Sausage War went unheeded.