qnli question: How many of the M2HB guns were mounted together on the M45 Quadmount weapons system? sentence: A plethora of anti-aircraft gun systems of smaller calibre were available to the German Wehrmacht combined forces, and among them the 1940-origin Flakvierling quadruple-20 mm-gun antiaircraft weapon system was one of the most often-seen weapons, seeing service on both land and sea.