The Big Blockade, also known as the Great Blockade, was a massive offensive carried out by Soviet forces against the Ukrainian Insurgent Army (UPA), from January to April 1946. The operation focused on the Carpathian Mountains, where a large part of UPA forces were deployed.

MVD troops were stationed in villages to prevent the local population from assisting UPA with supplies and food. At the same time, some 585,000 troops were sent into the forests and mountains to root out UPA fighters. Some 1500 major engagements were fought, and UPA faced not only huge numerical inferiority, but also heavy weaponry, armor, air attacks and bacteriological warfare. Almost half of UPA’s fighting forces were destroyed; after the Big Blockade UPA units were ordered to continue the struggle underground. Although the Big Blockade severely crippled the ability of UPA to engage in major operations, UPA continued to operate in the underground until at least 1952.