The article introduces an unknown memorial by P.I. Shuvalov of 1756, devoted to reforming irregular troops of Russian Empire. The authors analyze the context of the memorial, related to Russia’s entry into the Seven Years’ War and the mobilization capabilities of the military service corporation of the South-West, which should protect the south-western borders of the state from possible attacks by the Crimean Khanate, the Ottoman Empire and even the Polish-Lithuanian Commonwealth. The article shows that Shuvalov’s memorial was aimed at actual revision of rights and privileges of military service corporations in order to increase mobilization capabilities of Cossack troops. At the same time, P.I. Shuvalov, whose reform efforts at that time were also directed at the odnondvortsy, did not question the existence of the Landmilitia and irregular military service corporations as such, suggesting only to reform their management. However, the attempt at such reform did not yield significant results. One of the possible reasons was that such reform affected the interests of Ukrainian hetman K.G. Razumovsky. Mobilization problems that had place in the South-West during the Seven Years’ War led to a radical change in the government’s policy towards military service corporations under Catherine II.