A joint US-Australian search mission has located the four undetonated bombs that were dropped on to the Great Barrier Reef marine park in a botched military drill last month.

The Department of Defence said the royal Australian navy’s mine-hunter HMAS Gascoyne had located all of the ordnance on Friday.

The Australian navy will now help the US navy’s USS Germantown retrieve the bombs.

A Defence spokeswoman couldn’t confirm to Guardian Australia exactly when the retrieval would take place, but that it would depend on weather and environmental considerations.

The bombs were dropped into the sea by US aircraft that had run dangerously low on fuel. The aircraft were trying to bomb a small island in the Great Barrier Reef marine park in a drill conducted ahead of Talisman Saber, a biannual US-Australian training exercise that includes various war games.

After the mishap, the Great Barrier Reef Marine Park Authority said the bombs posed little risk to wildlife and had not been dropped on to a reef. But some local residents have voiced concerns about the environmental impacts of repeated military exercises so close to the reef.

Lieutenant General Ash Power, chief of joint operations, said the bombs had been found ahead of schedule at a depth of about 60m to 70m.

“HMAS Gascoyne has complied with all environmental regulations throughout the search and the bombs were positively identified using one of the mine-hunter’s remote operating vehicles,” he said.

“Our navy personnel have done a great job to locate these items very quickly and now stand ready to assist the retrieval process by the United States vessel USS Germantown.”