The first boat to sail was Щ 323, but it hit a mine between Leningrad and Kronstadt on 30.4. The boat sank with almost all of its crew, only five survivors. The boat was raised 1944, but it was so heavily damaged that it had to be scrapped [Pla04]. The boat had already been damaged by mines in 1942 when trying to cross the "Seeigel" barrier.
The second boat was Щ 303 that sailed from Lavansaari on 11.5. In the night of 14.5. the boat tried three times to sail under the net but failed. On 15.5. the boat tried to surface after being two days submerged but was caught by German barges. The boat tried to hide by laying in the bottom at Vaindlo. However, on 21.6. one of the men panicked, blew the tanks and jumped from the surfaced boat. Again, Щ 303 managed to escape and after a week of rest returned to Lavansaari on 8.6 [Ekm86],[Pla04].
While Щ 303 was escaping northwards the Finnish and German ships continued hunting. On 20. and 21.5. a submarine was detected around Vaindlo. On 22.5. Ruotsinsalmi and VMV 6 made an attack with depth charges that produced dead fishes and later some oil. The place was marked with a buoy and hunting continued. During the following two days the submarine tried to escape and hunters to maintain contact. On 24.5. the sister ship of Ruotsinsalmi, the Riilahti arrived and together the ships made a depth charge attack that produced oil, large air bubbles and debris. The destroyed boat was not Щ 303 as informed by the sailor that had deserted, but new Щ 408 that was on its first patrol [Ekm86].
26.5. another boat, Щ 406 was possibly sunk by german barges and Riilahti south from Porkkala-Kallbåda [Mer68]. A mine explosion had been noticed in "Nashorn" barrage and German barges dropped depth charges after which wood splinters and cork raised to the surface. Later on the same day Riilahti and barges dropped depth charges after which oil, large air bubbles and debris were seen. In Platonov the boat is said probably been destroyed by Finnish anti-submarine vessels 1.6. [Pla04].
The Щ-class boat had failed, and now it was time for the larger and more powerful S-class boats to try breaking to the Baltic Sea. The boats S 9 and S 12 sailed in the beginning of August. Neither of them reached Baltic Sea. Both of them were lost in the middle of August somewhere in or between "Seeigel" and "Nashorn" barrages. S 9 had signalled 10.8 that it will try to cross the net and 12.8. that it is returning. 4.9. body of one of its crewmembers was found on west shore of Seiskari [Pla04]. S 12 may have been destroyed by SAT Ost 5.8. west from Suur-Tytärsaari [Ekm83].
Of the five boats sent to Baltic Sea not a single one succeeded and only one returned. No ships were lost to submarines in 1943. The blocking of Gulf of Finland had been a 100% effective anti-submarine operation.