Hindu Military System of Orissa from the ancient times until it lost its independence in 1568 A.D. with particular emphasis on the imperial Gangas and the Suryavamsi Gajapatis who had built up a prosperous empire in the south eastern India. The traditional military system under the two famous and illustrious royal dynasties reached the highest watermark of glory and fame. Particularly under the Gajapati Kapilendradeva the empire was turned practically to a military state. Besides the four fold army, people irrespective of castes, creed, sects and sex participated in the war operations directly or indirectly for the safety and prosperity of their motherland. Despite the military strength, well established monarchy headed by great monarchs of such celebrated dynasties met ignominious fall in the hands of more powerful enemies repeating the historical process of rise and fall. The Gajapati empire, the last ever known in the annals of Orissa was disintegrated. The last Gajapati emperor Prataprudardeva was no match to the emperor Krishnadevaraya of Vijayanagar empire. In dealing with the military system of the Gangas and the Gajapatis author have attempted to refer, directly or indirectly to the contemporary Hindu kingdoms which subsequently supplemented the knowledge on the subject. Structurally the system was similar in almost all the Hindu kingdoms except the gigantic elephant force and the regional differences. However, the presentation is exhaustive and comprehensive, as far as possible, may not be construed to be conclusive. The work will be useful to the students of history, historians, archaeologists and art historians.