Mike Baker

Russia is facing a growing shortage of S-300 interceptor missiles.

Now, the S-300 system has been a cornerstone of Russian air defenses for decades and remains an important component of Moscow's layered network designed to protect military facilities and critical infrastructure and population centers.

Russia still possesses newer and more advanced systems, including the S-400 and the Pantsir platforms.

But officials cited by CBS News say stocks of S-300 interceptors have declined significantly.

And there are several reasons why.

First, Russia has spent years defending against an increasingly sophisticated Ukrainian drone campaign.

What began as relatively modest attacks has evolved into a sustained effort to strike deep inside Russian territory.

Ukrainian drones now routinely target refineries, fuel depots, air bases, logistics hubs and military production facilities hundreds of miles from the front lines.

Second, Ukrainian forces have made a concerted effort to target the actual Russian air defense systems.

Throughout occupied Crimea and other Russian-controlled territory, Kyiv has repeatedly struck radar installations and missile launchers and supporting infrastructure.

Every destroyed launcher represents not only a lost asset, but also, of course, fewer opportunities to intercept future attacks.

And finally, Russia has reportedly repurposed some S-300 missiles for offensive operations.

Originally designed as air defense interceptors, some have been modified for use as surface-to-surface weapons and fired against targets inside Ukraine.

Every missile used in that role is, of course, one less missile available to defend Russian airspace.

The result is an increasingly familiar problem.

Since the opening months of the war, Ukraine has repeatedly warned that it lacked enough interceptor missiles to defend every city and power plant, military base, and critical piece of infrastructure under threat.

Kyiv often found itself forced to prioritize.

Some targets received protection, while others remained exposed.

Now, there are growing signs that Russia may be confronting a similar challenge.

After all, Russia, of course, is a vast country.