A mysterious weather formation that appeared on the Bureau of Meteorology’s radar on Wednesday afternoon has been explained.

The large S-shape showed up off the Western Australian coast near Rottnest Island and was quickly dubbed by weather-watchers the “Rottnest monster”.



With experts initially stumped, conspiracy theorists stepped in to provide an explanation, suggesting the formation could have been alien spacecraft, the result of weather control experiments or, less tantalisingly, a well-synchronised flock of birds.



Now it appears the mystery has been solved.



On Thursday afternoon the defence department admitted it had been conducting exercises in the area.



A defence spokesman said the exercise was a training activity involving warships and aircraft, “designed to prepare a navy warship for an operations deployment”.



“The environmental conditions over the West Australian coast at the time of the activity provided a unique opportunity for this routine activity to be visible on the weather radar display,” he said.

