Pauline Hanson has been given a submarines 101 lesson by senior defence force officers.

The One Nation leader attempted to grill the officers about Australia's $50 billion submarine project during a Senate estimates hearing in Canberra on Wednesday.

French shipbuilder Naval Group has been awarded the design contract for a fleet of 12 vessels.

"Is it true that pump-jet submarines can only stay underwater for 20 minutes," Senator Hanson asked.

Rear Admiral Greg Sammut, who heads up the submarine program, patiently explained engineering features to the senator.

"A pump jet is a form of propeller, it has no bearing on how deep a submarine can go, how long it can stay under water," he said.

There were a number of factors including battery capacity that influenced time underwater.

"We are going to buy diesel-electric submarines and I can assure you senator they are going to stay underwater much longer than 20 minutes," Admiral Sammut said.

He declined to say how much longer, citing that information was classified because of operational security reasons.

"I don't think it's classified," Senator Hanson said.

The senator also cast doubts over the credentials of US experts who weighed up competing bids from France, Japan and Germany.

"America has not launched a diesel submarine for 55 years," she said.

Admiral Sammut insisted the US experts had a lot of experience in the operation of diesel submarines and so did Australia.

Naval Group's executive director of the Australian submarine program Jean-Michel Billig has said the vessels may end up with conventional propellers as well as air-independent propulsion.

John Madigan, a former independent senator, famously dubbed submarines the "spaceships of the ocean" in 2015.