In October 1917, the Russian Navy took its last stand. To gain complete dominance in the Baltic and finally lock up Russian ships at the bases, the Germans needed to capture the Moonsund archipelago. The Kriegsmarine command counted on an easy victory, believing that our fleet was completely demoralized by the suicidal "military reforms" of the Provisional Government and defeatist propaganda. However, contrary to all expectations, the Russian sailors put up desperate resistance to the enemy, writing another page in the annals of Russian military glory. The domestic reader knows about this feat mainly from the novel by Viktor Pikul "Moonsund" and the film of the same name. This edition presents the main documentary sources that the writer used when working on the book - an outstanding study of the Russian naval historian A.M. Kosinsky, which has not been reprinted since 1928, and the classic work of Admiral von Chishwitz, a participant in the Moonsund battle, representing the German point of view. A comparison of these sources provides the most complete, objective, "stereoscopic" picture of one of the most dramatic episodes of the First World War.