The day after Germany invaded the USSR, a German U-144, using its superior armaments, sank a Soviet M-98 sub, only to meet the same fate a month and a half later.

In this underwater war, the Soviet Navy won a narrow points victory, destroying four subs and losing three. The theaters of war were the cold waters of the Baltic and Barents Seas. Bona fide underwater duels were fought between the seamen. In his 2004 book Asy Podvodnoi Voiny (“Aces of the Underwater War”), Gennady Drozhzhin writes that out of all the active nine Kriegsmarine subs sank, four were destroyed by Soviet subs. One contemporary Russian historian claimed that in terms of German subs sunk, the Soviet Navy outdid all its Western allies. Therefore the decision to develop the submarine fleet was very logical: Relatively low production costs helped create a powerful force, capable of playing an important role in the war's naval battles. But the Soviet submarines could not compete with those from Germany, while the position of the UK (which had the biggest fleet in the world) in the event of a war was unclear. It was believed that after the beginning of the war the Soviet navy would be able to strike the enemy communications located in these regions. What remained were only closed seas: the Black Sea and the Baltic Sea. It had only two entrances to the open ocean, but both the North Pole and the Far East did not present the necessary possibilities to set up full naval infrastructure. Due to its geographical position the USSR could not fight for supremacy in the oceans. Nevertheless, the challenges placed before it were rather narrow. In terms of the number of subs it was twice as big as the fleet in the US and almost four times as big as the Kriegsmarine, the German navy. On the eve of the Great Patriotic War the Soviet submarine fleet was the largest in the world.

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