The joint exercise with the South Korean army was designed to develop the units ability deploy without notice and to integrate with local units.
The exercise was announced by US Forces Korea who confirmed the 18th Field Artillery Brigade, from North Carolina, carried out the live-fire exercise in Daecheon, South Korea.
Members of the artillery unit were given no notice before the being called on to rapidly deploy for the fire test.
A High Mobility Artillery Rocket System was fired at Jik-do Island off the coast of South Korea, the Eighth Army revealed.
Lt Gen Thomas Vandal said: ”This exercise shows Eighth Army’s ability to integrate joint capabilities with stateside units to any location on the Korean Peninsula in support of the ROK (South Korea)-US Alliance.”

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The latest escalation in tensions came as China issued a threat to South Korea to remove anti-missile systems deployed by the United States in the country.
Pyongyang also warned against the continued deployment saying South Korea was “digging up their own graves” by allowing the defence system to remain in the country.
Donald Trump ramped up economic pressure on North Korea to give up its nuclear weapons programme.
The US President announced plans to target any country trading with dictatorship through a new executive order.
Mr Trump said: “Our new executive order will cut off sources of revenue that fund North Korea’s efforts to develop the deadliest weapons known to humankind.”
Buoyed by Mr Trump’s promise to protect his allies from the Kim Jong-un’s missiles Seoul demanded the North abandon its nuclear arsenal immediately.
The office of South Korean President Moon Jae-in said: “We view the speech as portraying a firm and specific stance on the key issues regarding keeping peace and safety that the international community and the United Nations are faced with,”
“It clearly showed how seriously the United States government views North Korea’s nuclear programme as the president spent an unusual amount of time discussing the issue.”
President Trump used his speech to the United Nations to describe Kim Jong-un as his government as a “depraved regime” and a band of criminals.