In late February, when President Vladimir V. Putin of Russia declared that his country’s nuclear arms were entering “special combat readiness,” America’s surveillance gear went on high alert. Hundreds of imaging satellites, as well as other private and federal spacecraft, began looking for signs of heightened activity among Russia’s bombers, missiles, submarines and storage bunkers, which hold thousands of nuclear warheads.
The orbital fleet has yet to spot anything worthy of concern, image analysts said. Echoing the private assessments, U.S. and NATO officials have reported no signs that Russia is preparing for nuclear war. “We haven’t seen anything that’s made us adjust our posture, our nuclear posture,” Jake Sullivan, the national security adviser to President Biden, told reporters on March 23.
But America’s atomic watchdogs have reason to continue looking, experts said. Moscow has long practiced using relatively small nuclear blasts to offset battlefield losses. And some military experts are concerned over what Mr. Putin might do, after setbacks in Ukraine, to restore his reputation for edgy ruthlessness.
If Russia were preparing for atomic war, it would normally disperse its bombers to reduce their vulnerability to enemy attack, said Hans M. Kristensen, director of the Nuclear Information Project at the Federation of American Scientists, a private research organization in Washington. But right now, he said, “none of that’s evident.”
Since 1962, when one of America’s first spy satellites failed to spot a shipment of missiles and 158 nuclear warheads that Moscow had sent to Cuba, America’s surveillance powers in orbit have soared. Today, hundreds of public and private imaging satellites continually scan the planet to assess crops, map cities, manage forests and, increasingly, unveil the secretive doings of nuclear states.
Russia’s arsenal exceeds all other nations’ nuclear stockpiles in size, creating a challenge for analysts to thoroughly assess its state of play. Private American firms such as Maxar, Capella Space and Planet Labs have provided analysts with hundreds of close-up images of Russia’s atomic forces. Planet Labs alone has a constellation of more than 200 imaging satellites and has made a specialty of zeroing in on military sites.
The private fleet tracked Russia’s nuclear forces long before the war, revealing maintenance work as well as routine drills and exercises. That kind of baseline understanding helps analysts ferret out true war preparations, experts said. “You track this stuff and begin to get a sense of what normal looks like,” said Mark M. Lowenthal, a former C.I.A. assistant director for analysis. “If you see a deviation, you have to ask if something’s up.”
A false alarm rang shortly after Mr. Putin’s declaration. A Twitter account, The Lookout, posted that a satellite had spotted two Russian nuclear submarines leaving a northwestern port. The Express, a London tabloid, warned in a headline of “strategic readiness.” The news flash got little attention because seasoned experts realized the sub departure was a planned exercise.
Still, Jeffrey Lewis and Michael Duitsman, satellite image specialists at the Middlebury Institute of International Studies in Monterey, Calif., have continued to monitor Russia’s fleet of submarines because their movements can provide reliable indications of higher states of nuclear war readiness.
Normally, roughly half of Russia’s submarines equipped with long-range missiles go out to sea on scheduled patrols while the others remain at their piers for rest, repairs and maintenance. Analysts see empty piers as a warning sign.
To assess the current situation, Dr. Lewis zoomed in on a large submarine base known as Gadzhiyevo in Russia’s Arctic north. Images of it on Google Earth show a dozen massive piers jutting out from rocky fjords.
The Middlebury team examined a close-up image, taken by Planet on March 7, that showed four of Russia’s submarines alongside two of Gadzhiyevo’s piers. Mr. Duitsman said a separate image of the entire base revealed that all its active submarines were in port — suggesting they were not preparing for nuclear attack. “During a higher state of readiness,” he said, “I would expect several submarines to be out at sea.”
The team also studied images of a military base in the Siberian wilds where mobile launchers move long-range missiles on backcountry roads as a defensive tactic. Mr. Duitsman said the images — taken March 30 by one of Capella’s radar satellites, which can see through clouds as well as nighttime darkness — showed no signs of unusual activity.
Finally, near the banks of the southern Volga River, the Middlebury team looked at Saratov-63, a nuclear arms storage site for long-range missiles as well as Russia’s air force. A bomber base is nearby. The images, taken by Planet on March 6, revealed a snowy landscape and, Mr. Duitsman said, no evidence of a heightened alert status.
A senior American military officer in 1998 toured an underground bunker at Saratov-63 and reported that it held not only extremely powerful nuclear arms but also lesser ones, sometimes known as tactical weapons. The small arms are seen as playing lead roles in Russian nuclear strikes because their power can be fractions of the destructive force of the nuclear bomb in Hiroshima, Japan, blurring the line between conventional and nuclear arms and making them seem more usable.
Analysts and nuclear experts say the accumulating evidence suggests that Mr. Putin’s declaration of “combat readiness” was not an order to prepare weapons but rather a signal that a war message might be coming soon.
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Pavel Podvig, a longtime arms researcher from Russia, said the alert most likely primed the Russian military for the possibility of a nuclear order. Nikolai Sokov, a former Soviet diplomat who negotiated arms-control treaties, agreed. “It’s a signal to the command-and-control chain,” he said. “It simply means, ‘Come to attention. An order may be coming.’”
But Dr. Lewis of the Middlebury Institute said that Mr. Putin’s order also appeared to have sent more military personnel into central posts that relay orders and messages among dispersed forces. “That’s why we didn’t see anything,” he said. “It was increasing the number of humans in the bunkers.” The practice, he added, is a standard part of how Russia raises its levels of nuclear readiness: It takes more people to carry out war preparations than to maintain the sites in a standby mode.
Dr. Lowenthal, the former C.I.A. assistant director and now a senior lecturer at Johns Hopkins, said he found the personnel aspect of Moscow’s escalatory process the most troubling.
“We can develop a good baseline on what’s normal” and routine in the movement of Russian nuclear arms, he said. “It’s the internal stuff that’s always worrisome.” Imaging satellites, after all, cannot see what people are doing inside buildings and bunkers.
He said the main uncertainty was “the level of automaticity” in Russia’s escalatory war alerts — a topic addressed in “The Dead Hand,” a Pulitzer Prize-winning 2009 book that described a semiautomatic system meant to operate on its own in the event that Russia’s leaders had been killed. In that case, Russia’s nuclear authority would devolve to a few low-ranking officers in a concrete bunker. It’s unclear if Moscow today relies on something similar.
“You’re never quite sure” how Russia goes about authorizing the use of nuclear arms, Dr. Lowenthal said. “That’s the kind of thing that makes you nervous.”