The article highlights the issues of the underground activities of the OUN underground and the UPA fighters during the Second World War in Ukrainian historiography. The program and ideological documents of the Organization of Ukrainian Nationalists (OUN) are analyzed in relation to their vision of the role and place of Crimea in the geopolitical strategies of the future independent Ukrainian state. It is noted that back in the 20s–30s of the 20th century ideologists of the nationalist movement developed geostrategic concepts in which Crimea occupied a key place as a certain outpost of the Black Sea region, which cannot be conceded under any circumstances. It is noted that in these documents Ukrainian nationalists considered Crimea as the main base of the Ukrainian naval forces and the Ukrainian merchant fleet.It was established that Ukrainian nationalists began to implement their plans and own ideas in the conditions of the German-Soviet war, which is reflected in the works of Ukrainian historians and direct participants of those events. It is noted there that already at the beginning of July 1941, the first derivative groups of the OUN went to the central Ukrainian lands, from where they planned to take over all ethnic Ukrainian lands, creating their own authorities and administrations on them, and Crimea was one of their destinations. Accordingly, the OUN (Melnik’s supporters) and OUN (Bandera’s supporters) created special Crimean groups that were to move directly to the peninsula. In the autumn of 1941, the first groups of the OUN managed to enter the territory of the peninsula. At that time, the German occupation regime began repression against the members and supporters of the OUN, so the derivative groups moving to the Crimea were under the threat of exposure and physical destruction.It is noted that in Ukrainian historiography there is a widespread opinion, supported by the documentary base and eyewitness accounts, that Simferopol became the center of activity in Crimea. Separate structures of the OUN were also created in Dzhankoi, Yalta and other cities of the peninsula. Being persecuted by the German repressive authorities, Ukrainian nationalists were still able to gain a foothold in Crimea and start systematic organizational work, which consisted in creating a network of supporters, activities of cultural, educational and religious structures.It was established that in the conditions of Russia's full-scale invasion of Ukraine, the temporary occupation of part of the Ukrainian territory, including Crimea, comprehensive and unbiased coverage of the above-mentioned topic is a relevant and necessary matter today.