In September 1941, Bulgarian communist emigrés arrived on Soviet submarines and aircraft to boost the resistance movement. 55 experienced communist fighters were sent by the Foreign Bureau of the BCP, according to one version. According to another version, they were sent by order of the NKVD, of which the Bulgarian Communists in Moscow were not aware. The landing of the so-called ""paratroopers"" and ""submariners"" turned out to be precipitate and most of them were captured or killed. On the other hand, those who survived became some of the most prominent partisan leaders.