THE Senate inquiry into the children overboard affair may subpoena a senior naval commander who has spoken publicly about the issue despite being prevented from testifying at the inquiry.

Maritime Commander Rear Admiral Raydon Gates today said in Perth the navy's maritime command knew of reports suggesting an overloaded boat had left Indonesia for Australia on October 20 last year but took no action.

The boat sank, killing 353 people, and Rear Admiral Gates prepared a report on Australia's knowledge of it for the inquiry.

The inquiry, chaired by Senator Peter Cook, has been desperate to question the maritime commander on the issue but its requests for him to appear have eight times been rejected by Defence Minister Robert Hill.

Senator Cook said the inquiry was considering subpoenaing Rear Admiral Gates in the light of his public comments today.

"Given the refusal of the Defence Minister to have (Rear) Admiral Gates appear, I think it's a bit odd that he's openly canvassed all the issues relating to the inquiry in a public forum today," Senator Cook told AAP.

"In those circumstances, there's really no excuse for him not to front up before the committee."

He said the committee had asked Senator Hill's permission for Rear Admiral Gates to appear as a courtesy only, and would now consider approaching him directly.

The Senate inquiry was set up to examine the controversy surrounding reports that asylum seekers aboard a boat off Australia's north-west threw children overboard when intercepted by the warship HMAS Adelaide on October 7 last.

Defence and the government subsequently admitted the incident never occurred.

The committee's final report is due to be tabled in Parliament on August 21, but Senator Cook said it was not too late to reopen public hearings to hear from the maritime commander.

Rear Admiral Gates said today the overloaded boat, known as SIEV X, was one of nine boats the navy was tracking at the time and information about it was scanty.

"It was certainly not enough in my opinion as an operational commander to start to move assets to that effect," he said.

"We were still unconvinced, from my reading of it, that the thing had sailed on that date anyhow."

Rear Admiral Gates said that under the circumstances the navy was justified in not actively searching for the vessel.

"Let me stress to you it wasn't an oversight by the navy," he said.

The maritime commander said he did not believe it was necessary for him to testify at the Senate inquiry.

"What he (Senator Hill) was doing was emphasising to the inquiry that my information was second or third-hand and he could get for the inquiry, the people who had that information first-hand," he said.

"I was basically a conduit, an information-collector."

But Senator Cook said it was up to the committee to decide who should testify.

"It is not for him or the Minister for Defence to judge what his evidence might be - it's for us to judge according to our terms of reference," he said.