The first recoilless gun to enter service in Germany was the 7.5 cm Leichtgeschütz 40 ("light gun" '40), a simple 75 mm smoothbore recoilless gun developed to give German airborne troops artillery and anti-tank support that could be parachuted into battle. The 7.5cm LG 40 was found to be so useful during the invasion of Crete that Krupp and Rheinmetall set to work creating more powerful versions, respectively the 10.5 cm Leichtgeschütz 40 and 10.5 cm Leichtgeschütz 42. These weapons were loosely copied by the US Army. The Luftwaffe also showed great interest in aircraft-mounted recoilless weapons to allow their planes to attack tanks, fortified structures and ships. These included the unusual Düsenkanone 88, an 88mm recoilless rifle fed by a 10-round rotary cylinder and with the exhaust vent angled upwards at 51 degrees to the barrel so it could pass through the host aircraft's fuselage rather than risking a rear-vented backblast damaging the tail, and the Sondergerät SG104 "Münchhausen", a gargantuan 14-inch (355.6mm) weapon designed to be mounted under the fuselage of a Dornier Do 217. None of these systems proceeded beyond the prototype stage.