Recent studies of the Battle of the Ice (1242) in many respects derive from the late 1950s - early 1960s expedition of the Academy of Sciences of the USSR to the region of Lake Peipsi that was to determine the battle location. The reliability of the results it obtained is now evaluated differently, especially by those zealously searching for evidence of state commission. Materials collected and research carried out and published as early as 1962 is now used in disputes; however the authors contend that they are not sufficient for making balanced and objective conclusions. Handwritten diaries of the expedition leader G. N. Karaev should shed a new light on the history of the project: its preparation, field work progress, and applied methods. The diaries covering the period of 1956-1960 are stored in the fonds of the Archive of the Pskov State United Historical, Architectural, and Fine Arts Museum- Reserve. The text refers directly to the time of the described events (to a day). The diaries expound the research process (including submarine studies) and the general mood of the expedition. They show them the initiative came from the local historians, some of those amateurs. However, the support of leading scholars (particularly, academician M.N. Tikhomirov) and of the USSR Academy of Sciences gave the project its scientific force. The documents attached to the diaries confirm that G. N. Karayev founded his conclusions on the changes in level and depths of the lake, its bottom relief, and reasons for the absence of finds that definitely dated from the 13th century on the data obtained by experts in the natural and exact sciences. The authors conclude that the expedition journals of G. N. Karaev confirm the reliability of its results.