In order to transport to the area the necessary land and air forces, the maintenance of which is presupposed by Article 4 of the treaty, and in order to supply the forces in question, it is essential that an agreement be made between the USSR and Finland whereby Soviet trains will be allowed to travel on Finnish railways to and from Hanko.
Source: Finland reveals her secret documents on Soviet policy, March 1940—June 1941. Doc. nr. 18. Wilfred Funk, New York 1941.
The book is a verbatim translation of the "Blue-White Book" published by the Foreign Ministry of Finland, 1941.
Finland in the Soviet foreign policy 1939-1940