But seven drained-looking sailors emerged from the vessel that had held them captive for almost 76 hours yesterday after a British rescue robot cut them free in a six-hour, nerve-jangling operation that few Russians thought stood a chance.
In an emotional return to the world above the Pacific's grey obstacle-strewn waters, the mini-sub's commander, Vyacheslav Milashevsky, gave a long solemn salute to an expectant crowd as he came ashore in Russia's far east. His wife Elena said she had never felt so relieved. "I danced. I was glad, I cried and I danced for joy," she told Russian TV.
Sergey Ivanov, Russia's Defence Minister, broke his famously serious demeanour. "Great!" he exclaimed, delightedly shaking a clenched fist when he saw that the stubby red and white mini-sub had surfaced with all seven alive.
He called the survivors heroes, praised the Royal Navy and "the brotherhood of the sea" that had allowed the seven to be saved and set up meetings with the sailors' families.
The predicament the AS-28 Priz submersible found itself in since a combat training exercise went badly wrong on Thursday could not have been more serious.
The obstacles that pinned it 190m down and rendered its propeller useless were formidable. Fishing nets, cables and antennae which formed part of a huge underwater military submarine surveillance system, all weighed down with several anchors weighing 60 tons.
Commander Ian Riches, who led the British rescue team, said conditions inside were "pretty awful" as the oxygen supply ran out, the vessel filled with carbon dioxide and the temperature dropped below 5C. He thought the men had between 10 and 12 hours of oxygen left. They were forced to lie practically motionless to conserve their energy with lights off.
Admiral Viktor Fyodorov, commander of Russia's Pacific Fleet, said: "They behaved valiantly. We heard no complaints. All we heard was that they were fine. It is worth living for those moments."
An armada of 10 Russian ships had tried fruitlessly to drag the trapped submarine closer to shore and lift it up by looping cables around its body.
Mr Ivanov said the British took just six hours to cut five cables and clear obstacles including fishing nets. He blamed poachers for abandoning the nets. The Scorpio, flown from Glasgow on Saturday with a nine-strong crew and 20 staff including police, used its three underwater cameras and cable-cutters "relatively smoothly".
Admiral Fyodorov was generous with praise for the British. "With their excellent technical military equipment and their highest levels of professionalism, we bow before them. Their vessel made the difference. It would have been complex to save our sailors without such a vessel."