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Baffled: Recently retired Lieutenant Commander Barry Learoyd. Photo: Supplied

The ''inadvertent'' and repeated entry of Australian vessels into Indonesian territory defied comprehension, with the precise co-ordinates of the nation's maritime boundary typically programmed into the navy's electronic navigation systems, a former border protection commander has said.

The comments from Barry Learoyd, recently retired after a 43-year Royal Australian Navy career that included commanding vessels that interdicted asylum seeker boats, comes after a review into the incidents made the revelation that the vessels had not been given information about where Indonesia's sea border was situated

''It's really difficult to understand,'' Lieutenant Commander Learoyd said. ''The Indonesian archipelago and the archipelagic baseline [the formal name for Indonesia's maritime boundary] is well known to the Australian navy and well known to commanders and senior officers. It's part of the training we all get.''

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.''

Commander Learoyd said the finding was ''very surprising''.

Even so, the review blamed the crews on the vessels for the breaches, and navy and Customs commanders are facing disciplinary action, including possible demotion.

Operation Sovereign Borders is run not by the military but by the Customs and Border Protection Service. Its overall commander is Lieutenant General Angus Campbell, a three-star army general on secondment.

General Campbell was not at the headquarters when the highly delicate and difficult tow back operations took place, a Senate estimates hearing was told last week. Despite this, and the failure to provide vessels with the co-ordinates of Indonesia's maritime boundary, he has not been censured.

A Customs spokeswoman declined to say whether navy and Customs vessels had electronic navigation systems capable of being programmed with Indonesia's maritime borders. She also declined to confirm or deny, as reported by asylum seekers, that the vessels turned off their lights as they approached Indonesian territory to avoid detection.

Asylum seekers have claimed their own GPS systems indicated they were brought to within 7.5 nautical miles of Indonesia's land, well inside its maritime boundary.

The government has refused to say how far into Indonesian maritime territory the Australian vessels travelled, rebuffing requests for information from MPs during Senate estimates hearings. It is understood that three of the incursions were by two navy frigates, HMAS Parramatta and HMAS Stuart. The other three were by at least one Customs vessel.

Correction: An earlier version of this story incorrectly referred to Lieutenant-General Angus Campbell as a two-star general.

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