A Taipan crashed during the multinational Exercise Talisman Sabre last week off the north Queensland coast.
A recovery effort is under way for the bodies of Captain Danniel Lyon, Lieutenant Maxwell Nugent, Warrant Officer Class Two Joseph Laycock and Corporal Alexander Naggs.
Unidentified human remains have been found in the search for the army crew.
Pressed about why the helicopters were still in use despite documented problems, Mr Marles said Australia would be left with a capability gap if they were to all come out of service.
"To suggest we can just not have the capability on any given day is to not understand what the country faces," he told Nine's Today on Friday.
"We are transitioning them out and we are going down a path of having Black Hawks in place ... but it's not as though we are able to suspend the need for an airlift capability over a period of time before the Black Hawks are operational."
The defence minister said the choppers were certified to fly at the time of the crash.
Mr Marles said "idle speculation" would cause further harm to the friends and families of the dead ADF members.
"We need to make sure those helicopters are safe to fly," he said.
"What the families are owed is facts and proper investigations and not speculation.Â
"And that is what we will do."
The crash was the second incident involving a Taipan helicopter this year after another of the aircraft ditched off the NSW south coast in March during a training exercise.
The former coalition government announced in 2021 the fleet would be replaced by Black Hawks.
The Taipans are due to come out of service at the end of 2024.
The two-week Exercise Talisman Sabre involving Australia and 12 other nations is concluding on Friday.
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