To speed up the formation and training of a new army, the administration had decided to detach Russian officers and instructors from the lower ranks from the Danubian army to the Bulgarian units. Also, the Russian army encouraged the military training of the rural population in Russian units and Bulgarian voluntary detachments (which were called druzhinas) by all ranks. Such measures formed a mobilization reserve for the Bulgarian army. The Russian army had also delivered a significant amount of equipment and supplies to the Bulgarians. Russia actively contributed to the establishment of the Navy in Bulgaria. To train officers, capable young Bulgarians were detached both in Russian military schools and in the newly created Military school in Sofia. Costs incurred by the Russian exchequer for maintenance of the Temporary Russian Governance had to be reimbursed by the future Principality of Bulgaria and Eastern Rumelia. The sum accrued this way was called the "occupation debt". Bulgarians paid it irregularly, and its final settlement has taken almost half a century. The Principality of Bulgaria serviced the debt from 1883 until 1885, when relations between Bulgaria and Russia were severed after Bulgarian unification with Eastern Rumelia, which had not been approved by Russia, and the following Serbo-Bulgarian War, prior to which Russia had withdrawn its military officers, who had until that moment commanded all larger units of Bulgaria's young army. In 1890, it had sent a service payment, but regular payments were resumed only in 1896. Finally the "occupation debt" was paid off by the Principality of Bulgaria in 1902 at the expense of a large foreign loan issued by a bank Paribas. The occupation debt of Eastern Rumelia passed to the Principality of Bulgaria after the unification of Bulgaria in 1885. Its repayment was postponed many times until 1912, when Bulgaria and Russia agreed on a plan to repay the debt. The plan was never realized because after the beginning of the First World War the two countries were adversaries. After the war, the debt was written off by agreement between the Cabinet of Aleksandar Stamboliyski and the Bolshevik government of the Soviet Union. Eastern Rumelia  Military of Bulgaria  Principality of Bulgaria  History of Bulgaria  Russo-Turkish War of 1877–1878