By 1960, the combination of World War II and the massive emigration westward left East Germany with only 61% of its population of working age, compared to 70.5% before the war. The loss was disproportionately heavy among professionals: engineers, technicians, physicians, teachers, lawyers and skilled workers. The direct cost of manpower losses to East Germany (and corresponding gain to the West) has been estimated at $7 billion to $9 billion, with East German party leader Walter Ulbricht later claiming that West Germany owed him $17 billion in compensation, including reparations as well as manpower losses. In addition, the drain of East Germany's young population potentially cost it over 22.5 billion marks in lost educational investment. The brain drain of professionals had become so damaging to the political credibility and economic viability of East Germany that the re-securing of the German communist frontier was imperative.