submachine gun
US /ˈsʌb.mə.ʃiːn ˌɡʌn/
UK /ˈsʌb.mə.ʃiːn ˌɡʌn/

1.
a light automatic gun firing pistol-caliber ammunition, designed for close-quarters combat.
:
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The police officer carried a submachine gun during the raid.
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The soldiers were equipped with rifles and submachine guns.