Some of North Korea’s biggest howitzers have been spotted rolling across Russia on a train. It could be a sign that Pyongyang isn’t just supporting Russia with thousands of troops—it’s also sending artillery.

On Thursday, a photo circulated on social media depicting two M1989 Koksan 170-millimeter self-propelled howitzers on a train flatcar rolling through Krasnoyarsk in Siberia.

There are two likely possibilities: one, that a North Korean artillery unit is deploying to the front line in western Russia or Ukraine; two, that a Russian unit will operate the tracked, four-person howitzers, which can lob shells weighing 100 pounds or more at least 25 miles.

The latter makes more sense. So far, the Kremlin is folding North Korean troops into existing Russian units. The first few thousand North Koreans who trucked to the front line in Kursk Oblast in western Russia last month joined the ill-fated Russian 810th Naval Infantry Brigade.

Those North Koreans have yet to appear at the line of contact in significant numbers, but no one expects they won’t. For months now, the Russian military has been losing 1,500 to 2,000 troops a day, killed and wounded—a rate of loss that even the Kremlin, with its hefty enlistment bonuses and total control over the information environment in Russia, can sustain over the long term.

Russia needs foreign troops if it expects to keep up its war effort in Ukraine through next year. It needs foreign equipment, too. As the wider war on Ukraine grinds toward its fourth year, the stocks of old Cold War weaponry the Kremlin depends on to equip its regiments are running dangerously low.

Artillery stocks are dwindling at least as fast as stocks of tanks and fighting vehicles. A close survey of Russian military storage yards early this year counted 3,000 remaining self-propelled howitzers, down from 4,500 in 2021. And many of those remaining 3,000 guns were likely too corroded to be useful.

Some of the 1,500 self-propelled howitzers the Russians pulled out of long-term storage in 2022 and 2023 replaced the roughly 800 SPHs the Russians have lost in Ukraine. Others are equipping new units the Kremlin has formed since initiating the wider war in February 2022. Still others are being stripped for their parts—especially their carefully-milled gun barrels, which Russian industry struggles to build new.

Russian gunners would surely welcome a few batches of North Korean M1989s. They’re roughly analogous to the Russians’ biggest tracked howitzer, the 2S7. The Russians had around 300 2S7s in service or in storage as of 2022; a tenth of them have been knocked out or captured in battle, and many of the stored examples are beyond repair after sitting out in the open for decades.

The problem, from the point of view of the Russians, is ammunition. The M1989 is the only 170-millimeter howitzer in widespread use—and only North Korean industry makes ammunition for it. While Moscow has been buying shells from Pyongyang since early in the wider war, the Russians have also maintained their own domestic production for most calibers.

That’s impossible for those M1989s and their unique ammo. The giant guns will fire, or not fire, at Pyongyang’s whims. “Logistics have always been weak in the Russian army and the supplied howitzers may face a shortage of shells at some stage,” noted Artur Rehi, an Estonian soldier and analyst.

It’s further proof that, more and more, Russia depends on its allies—North Korea and also Iran—to sustain its war on Ukraine.