In Britain, the Royal Navy revealed that its submarines were suddenly having numerous encounters with Russian SSNs (nuclear attack subs). The Chinese and American navies are not revealing anything about similar encounters, but it appears that the Russians are updating their sound libraries. These are used for the passive (no broadcasting) sensors that subs favor. These sonar receptors listen for sounds, and compare ones that might be ships or subs, with previously recorded sounds in the sub's electronic library. Russian sonar sound libraries have long been in need of updating. Every ship, sub or marine animal has a distinct sound. Some American sound libraries can identify individual whales (these large mammals make a lot of noise).
All this activity is happening because Russian subs haven't been getting out to sea much in the last two decades. The Russian Navy has not only shrunk since the end of the Cold War in 1991, but it has also become much less active. Until about two years ago, Russian subs rarely came out to play. On average, only ten of their nuclear subs went to sea, on a combat patrol, each year. Most of the boats going out were SSNs (attack subs), the minority were SSBNs (ballistic missile boats). There were more short range training missions, which often lasted a few days, or just a few hours. But the true measure of a fleet is the "combat patrol" or "deployment." In the U.S. Navy, most of these last from 2-6 months. In the last three years, U.S. nuclear subs have carried out ten times as many patrols as their Russian counterparts. These long patrols are the ones where you can take the time to stalk the subs of potential enemy fleets, and capture their sound signatures.
The peak year for Russian nuclear sub patrols was 1984, when there were 230. That number rapidly declined until, in 2002, there were none. Since the late 1990s, the Russian navy has been hustling to try and reverse this decline. But the navy budget, despite recent increases, is not large enough to build new ships to replace the current Cold War era fleet that is falling apart. The rapid decline of Russia's nuclear submarine fleet needed international help to safely decommission over a hundred obsolete or worn out nuclear subs. This effort has been going on for a decade, and was driven by the Russian threat to just sink their older nuclear subs in the Arctic ocean. That might work with conventional ships, but there was an international uproar over what would happen with all those nuclear reactors sitting on the ocean floor forever. Russia generously offered to accept donations to fund a dismantling program that included safe disposal (of the nuclear reactors).
The Russian admirals made their big mistake in the early 1990s, when the dismantling of the Soviet Union left the second largest fleet in the world with only a fraction of its Cold War budget. Rather than immediately retire ninety percent of those ships, Russia tried to keep many of them operational. This consumed most of the navy budget, and didn't work. There were too many ships, not enough sailors and not enough money for maintenance or training at sea. The mighty Soviet fleet is mostly scrap now, or rusting hulks tied up at crumbling, out-of-the way naval bases. Since the end of the Cold War in 1991, most of the ship building money has gone into new nuclear subs. Six Akulas have been completed in that time, but the first of a new generation of SSBNs, the Borei class was delayed by technical problems, a new ballistic missile that wouldn't work, and lack of money. The first Borei class boat, after many delays, is finally ready for service, and ended up costing over two billion dollars.
Currently, Russia only has 14 SSBN (nuclear ballistic missile sub) boats in service, and not all of them have a full load of missiles. Some lack full crews, or have key systems in need of repair. Russia has only eight modern, 7,000 ton, Akula SSNs (nuclear attack subs) in service (another is leased to India). These began building in the late 1980s and are roughly comparable to the American Los Angeles class. All of the earlier Russian SSNs are trash, and most have been decommissioned. There are also eight SSGN (nuclear subs carrying cruise missiles) and 20 diesel electric boats. There is a new class of SSGNs under construction, but progress, and promised funding increases, have been slow. It's the Akulas that are shadowing the Royal Navy subs.
Currently, the U.S. has seven of the new, 7,700 ton, Virginia class SSNs in service, three under construction and plans to eventually build 30. The mainstay of the American submarine force is still the 6,100 ton Los Angeles-class SSN. Sixty-two of these submarines were built, 44 of which remain in front-line service, making it probably the largest class of nuclear submarines that will ever be built. The Seawolf-class of nuclear attack submarines stopped at three from a planned class of twenty-nine. The 8,600 ton Seawolf was designed as a super-submarine, designed to fight the Soviet Navy at its height. Reportedly, it is quieter going 40 kilometers an hour, than the Los Angeles-class submarines are at pier side.
While Western nuclear subs can last for about thirty years, Russian models rarely get past twenty. That means two new SSN or SSGN has to be put into service each year to maintain a force of forty boats. Unless the sub construction budget get billions more dollars a year, that is not going to happen. Right now, the priority is on producing a new class of SSBNs (11 more Boreis are planned or under construction). These Boreis are critical, because they carry SLBM (Sea Launched Ballistic Missiles) that provide a critical (they are much harder to destroy in a first strike than land based missiles) portion of the nuclear deterrent. The rest of the Russian armed forces, like most of the navy, is in sad shape, and unable to resist a major invasion. Only the ICBMs and SLBMs guarantee the safety of the state. So the way things are going now, in a decade or two, Russia will end up with a force consisting of a dozen SSNs and a dozen SSBNs.
The current fleet of nuclear subs is tiny, and the Russians have realized that if they don't get these boats to sea more often, the crews will become less capable to getting the job done in wartime. Given the number of accidents their subs have had in the past decade, it was obvious that the training the crews were getting was not sufficient. That has changed. The Russians subs are at sea three or four times more frequently than in the past two decades. Still not up to Western standards, but no longer in a downward spiral either.