The two AV-8B Harrier jets launched from aircraft carrier USS Bonhomme Richard each jettisoned an inert bomb and an unarmed explosive bomb in the World Heritage-listed marine park off the coast of Queensland state on Tuesday, the US 7th Fleet said in a statement yesterday.
The four bombs were dropped in more than 50 metres (164 feet) of water away from coral to minimise possible damage to the reef, the statement said. None exploded.
The jets from the 31st Marine Expeditionary Unit had intended to drop the ordnances on the Townshend Island bombing range but aborted the mission when controllers reported the area was not clear of hazards.
The emergency happened on the second day of the biennial joint training exercise Talisman Saber, which brings together 28,000 US and Australian military personnel over three week.
The US Navy and Marine Corps were working with Australian authorities to investigate the incident, the navy said.