The article reveals very important trends of Soviet military activity aiming at protection of the Baltic Sea coast of Estonia and Latvia in complicated political conditions of the Second World War outbreak. Appropriate articles by Soviet-Estonian and Soviet-Latvian mutual assistance pacts were accurately studied, as well as specific measures by National Navy Commissariat on construction of navy bases, forming of the squadron of warships, building coastal artillery batteries, airfields etc. The article is entirely based on archive material; it contains so far unknown facts about military and political situation in the Baltic Region in 1939-1940.