Strategic culture plays a significant role in shaping current practices of maritime security in Indonesia. Rooted in the history and experiences of the military and the state itself, Indonesian maritime strategic culture shapes the perceived roles and responsibilities of the Indonesian primary and most capable maritime security agency, the Tentara Nasional Indonesia Angkatan Laut. Albeit institutional, doctrinal reform and weapons modernisation, the navy appears to be reluctant to relinquish its long-standing law enforcement and internal security roles resulting in overlap of roles and responsibilities among the various maritime security agencies in Indonesia. This article argues that the historically shaped strategic culture, particularly the blurred distinction between ‘defence’ or sovereignty protection and ‘security’ or law enforcement, has not allowed the Tentara Nasional Indonesia Angkatan Laut to focus on the increasingly demanding traditional military roles. An understanding of Indonesian strategic history and culture as well as its civil-military relations is thus essential to comprehend this problem.