The Trans-Siberian railroad was a vital link across Siberia--in many cases, the only connection across the vast distance; railroads were even more vital in Russia than the rest of Europe for transporting units and supplies. Around Lake Baikal, the railroad hugged the coast of the lake and presented an ideal 'choke point' for cutting the tracks through sabotage and/or out-right attacks. There were a series of tunnels--seven, I believe(?)--through some of the biggest hills/mountains closest to the lake.
This image shows the general nature of the terrain.
Another image of Czech troops guarding a railroad tunnel on the Trans-Siberian railroad along Lake Baikal. The Communists cut the Czech Legion off from the friendly port of Vladivostok several times by dynamiting a tunnel or two. Nice image of Czech troops in Siberia fighting in Russian Revolution.
Written on the back of this card is "Destroyed RR bridge over River Onon by General Semenov"
