 Complete the following phrase:  Kite balloons began to be used at sea for anti-submarine purposes towards the end of World War I. The Red Army of the Soviet Union used Observation Balloons for artillery spotting. 8 Aeronautical Sections existed and 19,985 observation flights were performed by balloonists of the Red Army during the Second World War, clocking up 20,126 flight hours. 110 Soviet Observation Balloons were lost. Observation balloons also played a role during the Cold War; for example, Project Mogul used high-altitude observation balloons to monitor Soviet nuclear tests. However, heavier-than-air craft now performed the vast majority of operations. Aerostats have been used by US and coalition military forces in 