GIUK Gap Greenland-Iceland-UK Gap. The stretch of Atlantic Ocean running between Greenland, Iceland and the UK. Any Soviet ships from the Red Banner Northern Fleet intending to operate against NATO convoys have to cross this gap, making it a naval chokepoint. GRU Glavonye Razvedyvatelnoye Upravleniye. (Translation: Chief Intelligence Directorate of the General Staff), the Soviet military intelligence service. GPMG General Purpose Machine Gun.