How Was Russia Able to Launch Its Biggest Aerial Attack on Ukraine?

The 96-missile barrage fired across Ukraine on Tuesday was Russia’s biggest aerial attack of the war so far. But it followed months of assertions by Western and Ukrainian officials that Moscow’s stockpile of missiles and other weapons was rapidly dwindling.

Whether the assault on infrastructure targets was long planned, as Ukrainian commanders say they believe, or served as a deadly response to Kyiv’s recapture of the city of Kherson last week, the widespread attack raises questions about how much Russia’s arsenal may be depleted and whether Moscow will endure by finding alternative sources of weapons.

The Ukrainian defense minister, Oleksii Reznikov, said last month that Russia had burned though nearly 70 percent of its prewar cache of the kinds of missiles that were largely used in Tuesday’s attack: Iskander, Kalibr, and air-launched cruise missiles. At the time, Mr. Reznikov said that Russia had only 609 of those missiles left, though none of the figures could be independently verified.

An intelligence report by the British Defense Ministry dated Oct. 16 said that a large-scale attack on Ukrainian civilian infrastructure six days earlier had most likely degraded Russia’s long-range missile stocks, “which is likely to constrain their ability to strike the volume of targets they desire in future.”

Since spring, Pentagon officials have suggested that Moscow was low on precision-guided missiles, having run through its supply “at a pretty fast clip,” as a national security spokesman, John F. Kirby, said in May.

How, then, did Russia manage to launch what Linda Thomas-Greenfield, the U.S. ambassador to the United Nations, described as perhaps “the widest-scale missile attack since the beginning of the war”?

Here are four possible scenarios.

Russia is turning to Iran and North Korea for weapons, U.S. officials say.

At the Pentagon on Wednesday, Defense Secretary Lloyd J. Austin III said that Russia was struggling to replenish its missile stockpile to keep up with battlefield demands, “so they’re reaching out to Iran, they’re reaching out to North Korea.”

“I do think that those countries will probably provide them some capability,” Mr. Austin said.

The swarms of Iranian-made drones that are attacking Ukraine — most notably, the long-range Shahed series that can carry an 88-pound warhead and crash into targets in “kamikaze” strikes — have been Russia’s newest weapon in the conflict.

The Ukrainian Air Force said that it had shot down ten Shahed drones during Tuesday’s attacks.

This month, a spokesman for the Ukrainian Air Forces Command said that it was also expected that Iran would send ballistic missiles to Russia. The spokesman, Yurii Ihnat, said that it was unknown how many missiles Tehran might give Moscow, but he added that the weapons likely to be sent would be “fairly recently” manufactured, with a range of about 300 kilometers to 700 kilometers.

The United States has accused North Korea of secretly shipping rockets and artillery shells to Russia, although Mr. Kirby said this month that it was unclear if the munitions had been delivered.

Both North Korea and Iran have denied supplying Russia with weapons since the start of the war.

Russia may be building more missiles.

Last month, President Vladimir V. Putin of Russia announced domestic efforts to ramp up production of equipment and systems “associated with providing support for the special military operation” in Ukraine.

Janes, a defense intelligence firm, said that Russia very likely stockpiled microchips and other technology necessary to build precision missiles before invading Ukraine in February — possibly starting years ago, given Moscow’s deteriorating relations with the West after its illegal annexation of Crimea in 2014.

The Janes analysis, provided on Thursday to The New York Times, noted that such microelectronic components were also used for civilian purposes and that Russia may have obtained them through third parties, such as states or private entities that were willing to risk the penalty of U.S. sanctions if caught.

Russia probably began producing high numbers of Iskanders, Kalibrs, and cruise missiles before the invasion, the analysis said.

“They are likely being produced as we speak, since the economy is on a near war footing and many plants associated with the Russian military industrial complex are working in three shifts and even on weekends,” the Janes analysis said.

Russia is using air defense missiles to launch attacks, Ukraine says.

In a smaller follow-up strike on Thursday, Russia fired at least ten S-300 antiaircraft guided missiles against cities near the front line, according to the Ukrainian Air Force.

Built by Russia and exported across Asia and Eastern Europe — including to Iran and Syria, and to Crimea — the S-300 surface-to-air rocket was first designed in 1978 for protection against incoming air assaults. More recent generations of the missile can hit aircraft, drones and ballistic missiles.

But Russia’s increasing reliance on the S-300 as an attack weapon against ground targets in Ukraine has been one signal to military officials and experts that it is running out of its cruise missiles or other, more conventional offensive weapons.

Russia may have been holding some weapons in reserve for war against NATO.

Few, if any, Western officials have a clear account of the status of Russia’s arsenal or know precisely how many missiles remain in its stockpile, said Mark. F. Cancian, a former Marine and White House weapons strategist who is now at the Center for Strategic and International Studies in Washington.

But, he said, Western militaries believe that Russia has long kept a reserve of missiles and other weapons on hold in case it goes to war with NATO.

“They apparently have a withhold for a notional NATO attack,” Mr. Cancian said on Thursday, “which we would regard as absurd, but they regard it as a real possibility.”

“So they’re holding back some part of their inventory for that,” he said.

It is not known if Russia may have depended on those reserves for Tuesday’s strikes.