when they were deployed to the Western Front in 1917. These shotguns were fitted with bayonets and a heat shield so the barrel could be gripped while the bayonet was deployed. Shotguns fitted in this fashion became known as trench guns by the United States Army. Those without such modifications were known as riot guns. After World War I, the United States military began referring to all shotguns as riot guns. Due to the cramped conditions of trench warfare, the American shotguns were extremely effective. Germany even filed an official diplomatic protest against their use, alleging they violated the laws of warfare. The judge advocate general reviewed the protest, and it was rejected because the Germans protested use of lead shot (which would have been illegal) but military shot was plated. This is the only occasion the legality of the shotgun's use in warfare has been questioned. During World War II, the shotgun was not heavily used in the war in Europe by official military forces. However, the shotgun was a favorite weapon of Allied-supported partisans, such as the French Resistance. By contrast, in the Pacific theater, thick jungles and heavily fortified positions made the shotgun a favorite weapon of the United States Marines. Marines tended to use pump shotguns, since the pump action was less likely to jam in the humid and dirty conditions of the Pacific campaign. Similarly, the United States Navy used pump shotguns to guard ships when in port in Chinese harbors (e.g., Shanghai). The United States Army Air Forces also used pump shotguns to guard bombers and other aircraft against saboteurs when parked on airbases across the Pacific and on the West Coast of the United States. Pump and semi-automatic shotguns were used in marksmanship training, particularly for bomber gunners. The most common pump shotguns used for these duties were the 12-gauge Winchester Model 97 and Model 12. The break-open action, single barrel shotgun was used by the British Home Guard and U.S. home security forces. Notably, industrial centers (such as the Gopher State Steel Works) were guarded by National Guard soldiers with Winchester Model 37 12-gauge shotguns. Late 20th century to present Since the end of World War II, the shotgun has remained a specialty weapon for modern armies. It has been deployed for specialized tasks where its strengths were put to particularly good use. It was used to defend machine gun emplacements during