As soon as they appeared, aircraft dominated battlefields of the early 20th century. Anti-air weaponry was devised to target this new element specifically. The first real AA Gun was Gustav Krupp's 1-pounder gun modified to shoot down balloons, used in the Franco-Prussian War in 1870. At the beginning of WW I only several countries had anti-air weapons, but others quickly caught on, usually basing them on smaller field pieces - for example the French 75 mm and Russian 76.2 mm. Explosive and shrapnel ammunition was used. Targeting was a particularly dificult problem to solve due to the target's high maneuverability; a number of solutions were devised (like the Height/Range Finder device), but ultimately they were incapable of challenging the aircraft as equals. The subsequent introduction of radars and automatic targetting systems, based on electronics, and later, computers, dramatically improved the efficiency of AA Guns, but the developement of jet-propelled aircraft and guided missiles pushed them forever into a secondary role.