It is known that the depth of the Tatar Strait passage is not enough to pass large cargo boats, and only small ships can pass through it from Okhotsk Sea to Japan Sea, or sail from these waters through Amur River to Nicholaevsk-na-Amure and Komsomol'sk-na-Amure. Against such common sense, the Soviet government planned to dredge and prepare channels in the Amur Estuary so as to make them deep enough to pass large boats such as liberty ships. It was a very hard task, and the Construction Unit no. 201 under the NKVD had organized and engaged in this work, so much work was done by prisoners. The Unit had once dissolved in 1942, but in the next year, the Unit and its work were assumed by the Kommisarriat of Sea Transportation. The channels helped to navigate many cargo boats from the United States to the ports in the Russian Far East.
When World War II started, the US began to assist the Allied Powers, providing huge amount of materials useful to perform the war. After Nazi-Germany started war with the Soviet Union, the US began to assist the Soviet Union on large scale under lend-lease terms. The most used cargo route from the US to the Soviet Union was from West Coast of the US via North Pacific Ocean to Russian Far East ports, especially Vladivostok, After Japan started war with the US, Japan had limited navigation of foreign vessels through the Tsugaru Strait, so boats on this route had to pass the La Pérouse Straits or the Tatar Strait. The Japanese Navy watched the La Pérouse Strait carefully, but could not extend their eyes to the Tatar Strait and failed to grasp the situation of lend-lease aid to the Soviet Union. The Japanese government and Army had collected information on the lend-lease to the Soviet Union and analyzed it, but this was insufficient, and did not urge Japanese leaders to reconsider their hope of German victory, or later, achieving peace through the intermediation of the Soviet Union.