By Andrew Tilghman and Oriana Pawlyk, Staff writers

Early on the morning of Sept. 30, a Russian three-star general approached the American embassy in Baghdad, walked past a wall of well-armed Marines, to deliver face-to-face a diplomatic demarche to the United States. His statement was blunt: The Russia military would begin air strikes in neighboring Syria within the hour — and the American military should clear the area immediately.

It was a bout of brinksmanship between two nuclear-armed giants that the world has not seen in decades, and it has revived Cold War levels of suspicion, antagonism and gamesmanship.

With the launch of airstrikes in Syria, Russian President Vladimir Putin instigated a proxy war with the U.S., putting those nation’s powerful militaries in support of opposing sides of the multipolar conflict. And it’s a huge gamble for Moscow, experts say. “This is really quite difficult for them. It’s logistically complex. The Russians don’t have much in the way of long-range power projection capability,” said Mark Galeotti, a Russian security expert at New York University.

Moscow’s military campaign in Syria is relying on supply lines that require air corridors through both Iranian and Iraqi air space. The only alternatives are naval supply lines running from Crimea, requiring a passage of up to 10 days round-trip. How long that can be sustained is unclear.

That and other questions about Russian military capabilities and objectives are taking center stage as Putin shows a relentless willingness to use military force in a heavy-handed foreign policy aimed at restoring his nation’s stature as a world power. In that quest, he has raised the specter of resurgent Russian military might — from Ukraine to the Baltics, from Syria to the broader Middle East.

Russia’s increasingly aggressive posture has sparked a sweeping review among U.S. defense strategists of America’s military policies and contingency plans in the event of a conflict with the former Soviet state. Indeed, the Pentagon’s senior leaders are asking questions that have been set aside for more than 20 years:

• How much are the Russians truly capable of?
• Where precisely might a conflict with Russia occur?
• What would a war with Russia look like today?

Make no mistake: Experts agree that the U.S. military’s globe-spanning force would clobber the Russian military in any toe-to-toe conventional fight. But modern wars are not toe-to-toe conventional fights; geography, politics and terrain inevitably give one side an advantage.

Today, the U.S. spends nearly 10 times more than Russia on national defense. The U.S. operates 10 aircraft carriers; Russia has just one. And the U.S. military maintains a broad technological edge and a vastly superior ability to project power around the world.

Russia remains weak, according to many traditional criteria. But it is now developing some key technologies, new fighting tactics and a brazen geopolitical strategy that is aggressively undermining America’s 25-year claim to being the only truly global superpower. The result: Russia is unexpectedly re-emerging as America’s chief military rival.

As U.S. officials watch that unfold, they are “clearly motivated by concerns that at least locally, Russia has the potential to generate superior forces,” said David Ochmanek, a former Pentagon official who is now a defense analyst at the RAND Corp. And looming over the entire U.S.-Russian relationship are their nuclear arsenals. Russia has preserved, even modernized, its own “triad” with nuclear-tipped intercontinental ballistic missiles, a large fleet of long-range strike aircraft and increasingly sophisticated nuclear-armed submarines.

“The Russian defense industry is being rebuilt from ruins,” said Vadim Kozyulin, a military expert at the Moscow-based PIR Center, a think tank. “The military balance can only be ensured by Russia’s nuclear might, which isn’t as expensive to maintain as many people think.”

But while Russia’s conventional forces are less impressive than its nuclear forces, there are specific conventional areas where the Russians excel — among them aircraft, air defenses, submarines, and electronic warfare.

The Soviet-era weapons design bureaus remain prominent internationally. Russia’s aerospace industry, for example, has benefited greatly from international exports to non-Western nations, which go to Russia to buy effective fighter jets that are cheaper than their Western variants. China today spends more on defense annually than Russia, but still imports platforms and advanced weaponry from Russia.

Attempting a side-by-side comparisons of the U.S. and Russian militaries is a bit like comparing apples to oranges, many experts say; the Russians have distinctly different strategic goals, and their military structure reflects that. Russia views itself as a land-based power, exerting influence in a sphere expanding outward from its Eurasian heartland into Eastern Europe, Central Asia and possibly the Middle East and Pacific rim. It is well suited for relying on a particular set of capabilities known as “anti-access and area denial.”

“The United States and Russia are going for different things,” Galeotti said. “What the Russians are looking for is not to take on and compete on equal terms with us. It’s denial.” For example, he said, “one can look at the U.S. Navy as massively superior to the Russian navy. Most of them are legacy Soviet ships. But in a way, that doesn’t matter, because Russia does not plan to send its forces all across the world’s oceans.”

That’s reflected in the fact that Russia maintains a lone aircraft carrier while the U.S. Navy’s 10-carrier fleet operates on a continuing global deployment cycle. Instead of carriers designed for offensive power projection at sea, the Russians are investing in an expanding fleet of submarines that can supplement their nuclear force and, conventionally, threaten an enemy surface fleet in nearby waters such as the Black Sea, the Baltic Sea or the Mediterranean Sea.

Its airspace also is heavily fortified. The quality of Russia’s stealth aircraft is far weaker than those of the U.S., but Russia has cutting-edge anti-stealth systems, and also has invested heavily in robust surface-to-air missile systems and arrayed its forces domestically to protect its border regions. “The static airpower picture would favor the Russians because they have a lot of capability in terms of air defense and a variety of tactical and cruise and ballistic missiles,” said Paul Schwartz, a Russian military analyst at the Center for Strategic and International Studies.

Russia’s electronic warfare capability is also daunting to Pentagon military planners; left unclear is the extent to which Russia could jam the radars and signals intelligence that forms the foundation of the U.S.’s advanced air power. Any attempt by the U.S. and its allies to infiltrate Russian air space “would not necessarily be easy,” Schwartz said. “It would be a contested environment. But over time I think we would be able to degrade it. The problem is, with a nuclear power, you try to avoid a full-scale fighting.”

Meanwhile, the Russian army, still predominantly a conscripted force, is being transitioned to an American-style professional force. In effect, Russia has two armies: About two thirds of the roughly 800,000-man force remains filled with unmotivated and poorly trained draftees, but about one third is not — and those are the units outfitted with top-notch gear, including the Armata T-14 Main Battle Tanks.

In sum, the Russian military is not the equal of the U.S. military. But the gap has narrowed in recent years.