A rocket is a self-propelled, generally unguided, weapon-system powered by a rocket engine. Though used primarily as medium- and long-range artillery systems, historically rockets have also seen considerable use as air-to-surface weapons, some use as air-to-air weapons, and even (in a few cases) as surface-to-air devices. Examples of modern surface-to-surface rocket systems include the Soviet BM-27 Uragan and the American M270 Multiple Launch Rocket System.
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In military parlance, a rocket differs from a missile primarily by lacking an active guidance system; early missiles became known as "guided rockets" or "guided missiles". Some rockets were developed as unguided systems and later upgraded to guided versions, like the GMLRS, and these generally retain the term "rocket" instead of becoming "missiles". Rockets or missiles that travel underwater, like the VA-111 Shkval, are known as "torpedoes", whatever their propulsion system.