The Australian Navy has launched an investigation after a fire broke out aboard a submarine off Rockingham this afternoon.
The Defence Department said there were no injuries, but four personnel who were involved in fighting the blaze had been put ashore under medical observation as a precaution.
It is understood the incident took place a short distance from the HMAS Stirling naval base.
The fire broke out aboard HMAS Waller, a Collins Class submarine that had only recently returned to sea after a long period of maintenance.
The vessel was on the surface at the time. Other commercial vessels are believed to have been in the area as the drama played out.
There were no details given of how the fire may have begun.
"HMAS Waller had recently completed a scheduled maintenance period and was at sea as part of her return to operations," a Defence spokesman said.
"A full investigation into the incident will be held."
Australia's Collins Class fleet of submarines are based at HMAS Stirling but have been plagued with mechanical problems since they began service.
The Abbott Government is currently weighing how to replace the Collins Class fleet.