the 1920s, at a time when several Chinese warlords and their military factions running various parts of the fragmented country made purchases of the weapon and then subsequently produced many local copies). US troops were surprised to encounter communist Chinese troops armed with Thompsons (amongst other captured US-made Nationalist Chinese and American firearms), especially during unexpected night-time assaults which became a prominent Chinese combat tactic in the conflict. The gun's ability to deliver large quantities of short-range automatic assault fire proved very useful in both defense and assault during the early part of the war when it was constantly mobile and shifting back and forth. Many Chinese Thompsons were captured and placed into service with American soldiers and marines for the remaining period of the war. 1960s In the 1960s, Heckler & Koch developed the 9 mm Parabellum MP5 submachine gun. The MP5 is based on the G3 rifle and uses the same closed-bolt roller-delayed blowback operation system. This makes the MP5 more accurate than open-bolt SMGs, such as the Uzi. The MP5 is also one of the most widely used submachine guns in the world, having been adopted by 40 nations and numerous military, law enforcement, and security organizations. In 1969, Steyr introduced the MPi 69. This 9 mm Parabellum open-bolt, blowback-operated SMG has a telescoping bolt and is similar in appearance to the Uzi SMG. It has a vertical pistol-grip into which the magazine is inserted, a longer horizontal front grip area and a telescoping wire buttstock. The receiver is a squared stamped steel tube that partly nestles inside a large plastic molding (resembling a lower receiver) which contains the forward hand-grip, vertical pistol-grip and the fire control group, making the MPi 69 one of the first firearms to use a plastic construction in this way. It has a progressive trigger and is also unusual among modern SMGs, as the MPi 69 is cocked by a dual-purpose lever also used as the front sling attachment point. 1970s In the 1970s, extremely compact submachine guns, such as the .45ACP Mac-10 and .380 ACP Mac-11, were developed to be used with silencers or suppressors. While these SMGs received enormous publicity, and were prominently displayed in films and television, they were not widely adopted by military or law enforcement agencies. These smaller weapons led other manufacturers to develop their own compact SMGs, such as the Micro-UZI and the H&K MP5K. 1980s