Moreover, the co-ordinates of the boundary - which extends beyond the standard 12 nautical miles from Indonesia's coast at times - were usually in the electronic charting systems installed on navy vessels operating in the area, Commander Learoyd said.

''In the navigational display systems, you can overlay the boundary over your current position,'' he said. ''If that's not working, there are almanacs and manuals you can refer to.''

Customs and the navy released a heavily redacted version of its review into the incidents on February 19, describing each of the incursions as ''inadvertent'' and the ''result of miscalculation of Indonesian maritime boundaries by Australian crews'' .

But the review also said that neither the vessels tasked with turning back boats to the very edge of Indonesia's sea border, nor the headquarters overseeing the operations, were provided with information about where the boundary was actually situated.

''Indonesian maritime boundaries constituted important operational information that should have been provided by the headquarters to the commanders of vessels assigned to Operation Sovereign Borders,'' it said. ''This information should also have been available in the shore headquarters and used as a reference for task oversight and approval recommendations.''