After more than 30 years roaming quietly beneath the world's oceans, French nuclear attack submarine the Rubis is about a year away from a well-earned retirement.
Her missions are classified. But based on the type of operations these workhorses of the French navy have been doing in recent years, she might have patrolled the Caribbean Sea to stop drug smugglers, or if a merchant ship or oil rig were captured by pirates off Africa, French naval commandos might parachute into the sea from a plane to be picked up by the Rubis.
The submarine could then glide silently up to the hostage vessel and send the commandos swimming out through the torpedo tubes to board the vessel and overpower the pirates.
She might have captured vital intelligence on Muammar Gaddafi's regime from just off the Libyan coast. Or she might have provided protective muscle to the Charles de Gaulle aircraft carrier which has just returned from the Persian Gulf supporting air strikes against the Islamic State group. 
Or she might have scouted the seas to clear the way for the ultra-secret French ballistic missile submarines, her bigger cousins who provide a nuclear deterrence year round and whose precise whereabouts even the French President doesn't know at any given moment.
"It's what we call in French a 'couteau Suisse' - a Swiss army knife," said Admiral Louis-Michel Guillaume, France's submarine forces commander, after Fairfax Media was given a tour of the Rubis as it goes through maintenance at Toulon on the Mediterranean coast earlier this month.
"Every time there is a crisis in the world which is close to the sea, I have my phone ringing up and the operational vice-chief of the defence staff saying, 'Can I have a submarine to go there?'"
France is one of three bidders - the others being Germany and Japan - in what has turned into a Herculean contest to build Australia's new submarine fleet at a cost of at least $50 billion.
As feats of engineering, submarines are rivalled only by spacecraft. And despite the best efforts of anti-submarine technology, the silent killers retain a fundamental stealth edge by being underwater, invisible to radar.
With global maritime trade increasing, control of the seas is more important than ever - one reason China's maritime assertiveness is causing such anxiety.
In response, the global defence market has spoken: emerging nations are spending their newfound wealth building up submarine forces, meaning half the world's submarines will be in the Indo-Pacific region within 20 years.
Each of the Collins replacement bidders is fiercely spruiking their assets. Japan is running partly on its strategic advantages, in that a partnership would tighten the brotherhood of democracies against the unsettling rise of China. Germany is running as a safe pair of hands, having delivered 161 submarines to 20 navies before.
France is pushing its technical prowess and in particular its status as a complete submarine power, making large ballistic missile submarines, smaller nuclear attack submarines and conventional, diesel-electric boats - the type Australia wants to buy.
A tour of French shipbuilder DCNS's shipyard at Cherbourg on France's channel coast shows the mammoth effort involved in designing and building a submarine.
The incomplete first boat of the new Barracuda class, named the Suffren - which will replace the Rubis next year - sits in a massive factory, naked-looking and covered in wiring, pipes and holes over which the outer pressure hull will be welded.
It is 100 metres long, has about 1 million components and will take 8 million man hours to construct. A car has about 3000 components and takes 23 man hours to make.
"The submarine is the most difficult thing in the world to make," explains Olivier Theret, who heads a team of 70 engineers doing testing and quality control. "The final objective is the safety of the person on board; they're the ones who sign up to go out there."
Theret tests everything that will go into the Barracudas. He has plates of steel sitting in salt water for up to 20 years to test for corrosion. He tests the welding work up to leak tolerances of three microns - narrower than the width of a human red blood cell.
In a neighbouring factory, steel sheets up to 20 centimetres thick are cut using super-high-pressure water jets containing gritty particles, which unlike a blowtorch don't damage the metal. The steel is then shaped into hull sections using massive presses that exert 12,000 tonnes of pressure.
Submariners themselves have already helped fine-tune the interior of the Suffren using virtual reality that allows them to walk around and get a feel for it. They've made thousands of suggestions to the design team.
All of this would have to be replicated in Australia if - as is virtually certain unless the government has lost its political marbles - the bulk of the construction work is done at the ASC shipyards in Adelaide. DCNS says a largely Australian construction would create 2900 direct jobs in Australia.
Australia's submarine needs are very particular, requiring a long range to reach places like the South China Sea but without the endurance of nuclear power. Without a local nuclear industry, Australia is stuck with buying conventional diesel-electric boats, which are slower over long distances and cannot stay underwater indefinitely.
France is proposing a conventional version of the Barracuda class, which sounds rather like asking a horse to pull a Ferrari, though DCNS chairman Herve Guillou said last week the conversion was "very easy" and has been done before.
The other bidders face technical challenges as well. The Japanese Soryu submarine doesn't go far enough for Australia's needs. Its endurance must be improved.
DCNS's top executives caused ripples last week when they suggested the Japanese are rushing ahead with high-tech lithium ion batteries - despite being unproven and therefore possibly dangerous - because otherwise the Japanese boat won't go far enough.
The Germans meanwhile have never built a submarine as big as the one Australia needs.
On top of all this, Jacques Cousquer, Asia-Pacific director for the procurement branch of France's Defence Ministry, said that margins have to be built into new submarines so they can be updated and evolved over the next 30 to 40 years. This will include everything from improved sonars to better hull stealth coating to the ability to launch swarms of underwater robots.
"This is important because the threat is moving ??? and if you wake up and discover a new threat that you haven't thought about yesterday, it'd be a pity," Cousquer said.
Somehow all this knowledge and expertise must in turn be transferred to Australians so that we have some sovereignty over the technology and in particular the ability to maintain the boats.
Australia isn't just buying a submarine, it's entering a technological marriage with another country for decades to come. The increasingly fractious public battle between the bidders - evidenced last week by DCNS's swipe at the Japanese over lithium ion batteries - suggests that marriage might be as complex as the futuristic submarines themselves.