they were used as a weapon in themselves. Dog fights erupted in the skies over the front lines, and aircraft went down in flames. From this air-to-air combat, the need grew for better aircraft and gun armament. Aside from machine guns, air-to-air rockets were also used, such as the Le Prieur rocket against balloons and airships. Recoilless rifles and autocannons were also attempted, but they pushed early fighters to unsafe limits while bringing negligible returns, with the German Becker 20mm autocannon being fitted to a few twin-engined Luftstreitkräfte G-series medium bombers for offensive needs, and at least one late-war Kaiserliche Marine zeppelin for defense – the uniquely armed SPAD S.XII single-seat fighter carried one Vickers machine gun and a special, hand-operated semi-automatic 37mm gun firing through a hollow propeller shaft. Another innovation was air-to-air bombing if a fighter had been fortunate enough to climb higher than an airship. The Ranken dart was designed just for this opportunity. This need for improvement was not limited to air-to-air combat. On the ground, methods developed before the war were being used to deter enemy aircraft from observation and bombing. Anti-aircraft artillery rounds were fired into the air and exploded into clouds of smoke and fragmentation, called archie by the British. Anti-aircraft artillery defenses were increasingly used around observation balloons, which became frequent targets of enemy fighters equipped with special incendiary bullets. Because balloons were so flammable, due to the hydrogen used to inflate them, observers were given parachutes, enabling them to jump to safety. Ironically, only a few aircrew had this option, due in part to a mistaken belief they inhibited aggressiveness, and in part to their significant weight. First shooting-down of an aeroplane by anti-aircraft artillery During a bombing raid over Kragujevac on 30 September 1915, private Radoje Ljutovac of the Serbian Army successfully shot down one of the three aircraft. Ljutovac used a slightly modified Turkish cannon captured some years previously. This was the first time that a military aeroplane was shot down with ground-to-air artillery fire, and thus a crucial moment in anti-aircraft warfare. Bombing and reconnaissance As the stalemate developed on the ground, with both sides unable to advance even a few hundred yards without a major battle and thousands of casualties, aircraft became greatly valued for their role gathering intelligence on enemy positions and bombing the enemy's supplies behind the trench lines. Large aircraft with a pilot and