Among the air units of the Northern Fleet was the 121st Fighter Aviation Regiment. The Northern Fleet was reinforced with naval aircraft and ships from the Pacific Ocean and Caspian Sea. Great Britain and the United States temporarily provided HMS "Royal Sovereign" and to the USSR in exchange for the Italian ships captured during the war and destined to be divided among the allies. During the war, the Northern Fleet secured safe passage for 1,463 ships in external convoys and 2,568 ships in internal convoys. Its submarines, torpedo boats, and aviation sank 192 enemy transport ships and 70 other hostile military ships. The Northern Fleet also damaged a total of 118 transport, military, and auxiliary ships. Soviet submarine "K-21", under the command of Captain Nikolai Lunin, attacked the German battleship "Tirpitz" at 71° 22' 2"N, 24° 34' 3"E. The К-21 logbook reports observation of two torpedo explosions, but no damage is reported by German sources.