A strange, S-shaped object, which appeared on a Bureau of Meteorology radar map off the west coast of Australia on Wednesday afternoon, left meteorologists baffled and set the rumour mill churning.

The snake-like formation, located about 18 miles off the coast, was dubbed the “Rott Nest Monster” across social networking sites, as users wondered about its origin.

On Twitter, @harbinger451 tweeted: “A flying snake heads towards Perth.”

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And @David_Coombe said: “BOM radar produces many anomalies, though the #rottnestmonster is fun.”

In an interview with the ABC, meteorologist Neil Bennett said the phenomenon could not have been a cloud. “They don’t take on S shapes and things like that,” he said.

“The radar that we use are there for the detection of precipitation, it's basically just a beam going out and hitting the rain droplets or ice particles from hail.

"Sometimes the beam itself rather than going straight it gets bent back to earth and you start to pick up reflections from the ocean, rather than rain droplets," he added.

But the Department of Defence today confirmed that the enigmatic snake was in fact caused by a military exercise.

A spokesman for the Department of Defence told ABC News that the exercise was a regular training activity involving ships and aircraft designed to prepare a Navy warship for an operational 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.

"This exercise is ongoing."