A strange detail noticed at the funeral of the 14 people killed in Russia's latest submarine disaster has raised questions about the massive risk run by the sub's "dark" mission.
Just what was that secret Russian midget submarine doing before it caught fire? One officer said its 14 dead crew prevented "planetary catastrophe". But was it actually engaged in a clandestine war?
The mystery began on the evening of July 1.
Fishermen reported seeing a submarine suddenly surface near Ura Bay, just 100km on the
Russian side of its border with Norway.
Moscow won't admit it, but Russian news outlets have reported the submarine to have been the top-secret AS-31 Losharik.
Whatever it was doing, it was something special.
We know this because Moscow has made a point of telling us nothing about it.
"It belongs to the highest level of classified data, so it is absolutely normal for it not to be disclosed," a Kremlin spokesman said when refusing to identify the submarine.
But not even President Vladimir Putin was able to suppress the news that the damaged vessel had been towed into Russia's Northern Fleet Headquarters at Severomorsk.
And then there was the 14 crew who needed to be buried.
Western defence analysts are scrambling to infer what they can from the minimal information at hand.
Losharik was a secret project. It was nuclear powered, giving it high speed and endurance. It was an unusual, experimental design. It was intended to dive very deep.
What possible missions could benefit from such attributes? How could it contribute to "planetary catastrophe"?
According to the Moscow Times, a high-ranking officer made the extraordinary statement at the funeral of the 14 crew who reportedly died from smoke inhalation after what some speculate may have been a fire in the submarine's battery compartment.
"With their lives, (the 14 sailors) saved their comrades, saved the ship and averted a catastrophe of planetary scale," the independent Open Media reported an unnamed high-ranking military official as saying at the weekend funeral.
Mr Putin admitted on Friday that the minisub was nuclear powered. His defence minister immediately assured the public the "heroic" crew had sealed off the reactor before they died, preventing radiation risk.
Speculation, however, remains rife. Much has been made on social media of footage showing the sailors' coffins, and their apparent weight on pallbearer's shoulders.
Were they lead-lined? Or was the double-handed poise pallbearers adopted simply a mark of respect?
Norway reported shortly after the incident that Russian officials had reported an incident aboard the submarine involving a "gas" explosion. Moscow quickly moved to deny this.
Since then, Norway has reported no trace of increased radiation levels on its northern border.
Moscow's Ministry of Defence said the midget submarine at the centre of the tragedy was "designed to study the bottom space and the bottom of the ocean in the interests of the Russian Navy," though it did not name the vessel.
And bathymetric surveys (mapping the ocean floor) is a standard cover for covert operations.
Losharik was launched in 2003. Since then, it's mostly been kept out of the public limelight.
It is smaller than most nuclear-powered submarines, at just 60m long, carrying a crew of only 25. Russian media has in the past reported it was designed to be carried beneath a bigger "mother" submarine, such as the recently launched Belgorod class.
This behemoth is being touted as being capable of carrying Mr Putin's huge new "Poseidon" tsunami-generating super-weapon.
One such "mothership", the Podmoskovye, is believed to have been operating with Losharik at the time of the accident. And both are crewed by elite personnel belonging to a special intelligence unit of the Russian Navy called the Main Directorate of Deep-Sea Research.
The military potential for such a combination — with the bigger submarine carrying the smaller deep-diving vessel anywhere in the world — has been the cause of great concern in the West.
In 2016, US Northern Command named it a "dark" threat needing the development of new undersea monitoring technologies to protect vital subsurface assets.
Reports suggest Losharik was capable of diving to the extraordinary depth of 2500 meters. Its odd design of seven linked spherical titanium chambers supports this claim.
This has helped fuel speculation that it was designed explicitly with undersea cables in mind.
For years, Russia has been observed displaying an unhealthy interest in undersea internet cables. Why?
"The tactical reasons for doing so are plain," former US Admiral Jim Stavridis told The Huffington Post. "In the case of heightened tensions, access to the underwater cable system represents a rich trove of intelligence, a potential major disruption to an enemy's economy and a symbolic chest thump for the Russian Navy."
This has the West worried. So nations such as the US, UK and Australia have since been paying extra attention to the movements of Moscow's submarines.
After all, much of the world's economy now relies on the almost instantaneous communications offered by the world wide web. Forget satellites. Cables carry 97 per cent of all global communications at any one time.
Beneath the sea, things have quickly heated up. Naval analysts say the deadly Cold War-era games of cat-and-mouse are back.
But tapping or cutting undersea cables is nothing like the hunter-prey stalking of submarine movies.
Instead, it requires small specialist submarines secretly diving to great depths. Tamper with a cable down there, and it's so much harder to locate or repair. It's a job that needs precision. Care. And all under the enormous pressure of the ocean stacked above.
The full tale of Losharik is nowhere near being told.
"It came out of the water, all of it," one fisherman told Murmansk-based media. "I'd never seen anything like that before … There were people running, rushing on the deck."
What caused the fire? What task was the boat engaged in that could create such an event?
"The submariners acted heroically in the critical situation," Defence Minister Sergei Shoigu said. "They evacuated a civilian expert from the compartment that was engulfed by fire and shut the door to prevent the fire from spreading further and fought for the ship's survival until the end."
Among the dead were seven holding the rank of captain. Typically, such a vessel only carries one.
This only raises more questions. Why was a civilian aboard? Was it testing a new piece of equipment? Why were so many senior officers present?
Whatever the Losharik was up to, the Kremlin wants it doing it again. And fast.
Mr Putin cancelled his schedule and ordered his defence minister to "personally" investigate the incident.
The Moscow Times quotes Mr Shoigu as stating the "special purpose" submarine was to be fully restored and returned to service.
"The constructors of the vessel and industry representatives have been engaged to estimate the work volume and time needed for the ship restoration," Shoigu said. "Our first assessment shows that repair is possible, (and) in our case it is not only possible but absolutely required."
This was mostly possible because the compartment housing the submarine's single nuclear reactor had been unaffected by the accident, he said.
"The crew took all required measures to protect the installation, it is in a fully working condition, and this makes us hope that the vessel can be restored in a short time."