The German invasion of the Soviet-Union has started 22 june 1941 and the end of August Tallinn is surrounded by German troops. On August 27 the evacuation of the Russian Baltic Fleet started. With this evacuation the Russian lost many people (12.000) and ships.
The handbook about this period:
Estland Handbuch Philatelie, Kommunikations – und Postgeschichte : Estland vor dem (Juli 1941 – 30.11.1941) und als Teil vom Generalpostkommissariat OSTLAND (01.12.1941 – Setember 1944) = Estonia Handbook of Philately and Postal History : Estonia before (July 1941 – 30.11.1941) and as part of the “Generalpostkommissariat OSTLAND” (01.12.1941 – September 1944) / Herausgegeben von Harry v. Hofmann . – Hamburg : Harry v. Hofmann Verlag, 2010. – 472 p.