 In Colombia, Israel, Norway, Singapore, South Korea, Sweden and Taiwan service in the reserves is compulsory for a number of years after one has completed national service.A military reserve force is different from a reserve formation, sometimes called a military reserve, a group of military personnel or units not committed to a battle by their commander so that they are available to address unforeseen situations, bolster defences, or exploit opportunities.During the eighteenth century, some nations' military systems included practices and institutions that functioned effectively as a reserve force, even if they were not specifically designated as such.