▁mines ▁on ▁ 3 0 ▁April ▁ 1 9 4 3 ▁( five ▁surv iv ors ). ▁Sh Ch - 3 0 3 ▁failed ▁to ▁pass ▁the ▁n ets ▁and ▁returned ▁to ▁Lav ans a ari ▁after ▁enc oun ters ▁with ▁German ▁vessels . ▁Sh Ch - 4 0 8 ▁was ▁detected ▁and ▁s unk ▁by ▁Finn ish ▁min el ayer ▁Ru ots ins al mi ▁with ▁depth ▁charges , ▁while ▁Sh Ch - 4 0 6 ▁suffered ▁the ▁same ▁fate ▁by ▁Finn ish ▁min el ayer ▁Ri ila ht i ▁and ▁German ▁small ▁boats . ▁ ▁After ▁the ▁fail ures ▁of ▁the ▁Sh ch uka - class , ▁the ▁S ovi ets ▁attempted ▁to ▁break through ▁with ▁the ▁more ▁powerful ▁S - 9 ▁and ▁S - 1 2 : ▁both ▁of ▁them ▁never ▁returned ▁and ▁were ▁lost ▁to ▁mines ▁in ▁August ▁ 1 9 4 3 , ▁mark ing ▁an ▁end ▁of ▁the ▁S ovi ets ▁attempt ▁to ▁pen et rate ▁the ▁block ade . ▁ ▁After math ▁▁ ▁The ▁Finn ish ▁min el ay ers ▁Ru ots ins al mi ▁and ▁Ri ila ht i ▁has ▁been ▁act ively ▁engaged ▁in ▁the ▁campaign , ▁s inking ▁one ▁sub marine ▁each . ▁ ▁On ▁ 2 3 ▁August ▁ 1 9 4 3 , ▁during ▁another ▁anti - sub marine ▁pat rol , ▁Ri ila ht i ▁was ▁s unk ▁by ▁sovi et ▁motor ▁tor ped o ▁boat ▁T K - 9 3 . ▁ ▁Out come ▁ ▁No ▁Soviet ▁attempt ▁to