KYIV, Ukraine – Russia and Belarus have launched the largest joint military exercises since the Cold War, with 30,000 Russian troops taking part, according to U.S. military estimates. 

Many nervous NATO allies wonder what comes next when the drills end on Feb. 20th. Will the Russian troops go home or invade Ukraine and take over the capital city and topple the government? 

"This is probably the most dangerous moment," said British Prime Minister Boris Johnson at NATO headquarters Thursday, "in what is the biggest security crisis that Europe has faced for decades." 

"This is a dangerous moment for European security. The number of Russian forces is going up. The warning time for a possible attack is going down," NATO Secretary-General Jens Stoltenberg said at a news conference alongside Johnson in Brussels.

Russian President Vladimir Putin gestures while speaking at an extended meeting of the Russian Defense Ministry Board at the National Defense Control Center in Moscow, Russia, Dec. 21, 2021.

Russian President Vladimir Putin gestures while speaking at an extended meeting of the Russian Defense Ministry Board at the National Defense Control Center in Moscow, Russia, Dec. 21, 2021.  (Sergey Guneyev, Sputnik, Kremlin Pool Photo via AP, File)

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The U.S. Embassy in Ukraine announced Friday that the 14th flight of weapons had arrived in Kyiv, including more Javelin anti-tank missiles. 

Russia's top officer, Gen. Valery Gerasimov, has flown to Belarus to personally oversee the joint exercises with Russia’s ally. American Gen. Mark Milley, chairman of the Joint Chiefs of Staff, spoke to his counterpart in Belarus by phone Thursday to "reduce chances of miscalculation," according to the Pentagon. He also spoke to his British and Ukrainian counterparts.  

Russian amphibious warships are now in the Black Sea. Ukraine's defense minister said Russia has now "blocked" waters offshore ahead of planned missile tests in the coming days. Many of Russia’s large warships in the Black Sea are loaded with naval infantry, tanks and other armored units.  

A former top commander of U.S. Army forces in Europe believes Russia is most likely to strike Ukraine from the sea. 

"It will be a little bit below some perceived threshold where not every European country will be so thrilled about having to invoke sanctions ‘like you've never seen before’ because Russia took some islands or coastal area," said retired Lt. Gen. Ben Hodges, now the Pershing Chair at the Center for European Policy Analysis.   

"What the Russians are doing is like a boa constrictor that is continuing to squeeze Ukraine," Hodges added. He does not expect the massive, full-scale invasion of Ukraine that many in Washington predict. 

"I don't anticipate an all-out assault with these red arrows that we've been seeing pictures in newspapers, red arrows coming in from every direction simultaneously. I don't know that the Russians have the assets." 

Sen. Tom Cotton, R-Ark., a former Army infantry officer with combat deployments to Iraq and Afghanistan, disagrees. 

"I think the invasion is much more likely than not. I very much respect Gen. Ben Hodges. It is true that southeastern Ukraine and Mariupol are very exposed, but it’s also true that the capital city Kyiv in central Ukraine is exposed to those military exercises in Belarus," Cotton said during a live interview on the Fox News Channel with Sandra Smith. "Those military drills in Belarus, Sandra, are nothing but a cover for a likely invasion."

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Like President Biden, Cotton advised all Americans in Ukraine to "leave today." 

It’s not just Russian forces on the move. American B-52 bombers arrived in England Thursday. The Pentagon called the deployment "long-planned." The U.S. Air Force also announced it was sending F-15 fighter jets to Poland to help bolster NATO defenses one day after the White House approved plans for some of the 3,000 U.S. troops sent to Poland to help set up camps on the border to assist with a potential invasion of some 30,000 Americans in Ukraine, should Putin order an invasion. 

Since 1999, when NATO expanded to include three former Warsaw Pact countries, Russia has seen the alliance expand closer to its borders. Russian President Vladimir Putin has said he feels threatened, pointing to the bombing of Serbia three weeks after Poland, Hungary and the Czech Republic joined NATO as proof the alliance is not always "defensive" as the West claims. Putin has also cited NATO operations in Libya and Iraq as more examples of what he calls overreach.  

Since retiring as head of U.S. Army Europe, Hodges called the technological advancement of the Russian forces in recent years "chilling." 

"The ability to develop their drones, to connect drones, to detecting targets on the ground either from intercept or through visual, and then have artillery or rockets hit that target so quickly, that is one of the most chilling capabilities to realize that they have that, and clearly that matured a lot while they were in Syria." 

Russian forces first deployed to Syria in 2015.  Since then, Russia has used the opportunity to showcase its vast array of new weapons, such as launching guided Caliber missiles from warships, the same way U.S. Navy destroyers have launched Tomahawk cruise missiles in recent decades. 

Before going to the Black Sea, the Russian warships stopped to resupply in the Syrian port city of Tartus on the Mediterranean coast.

"We look at Russia as a pure adversary [now]," Hodges said.  

"I am very impressed and concerned with the development of Russia's electronic warfare capability. You know, the last 20 years, we were focused correctly, on cellphones, and terrorist networks and in trying to intercept and crack into those," Hodges said. "Meanwhile, Russia continued to develop high-end electronic warfare capability that enables them to intercept, but more importantly, jam at long distances – to jam communications, satellites, etc."

Ukraine Army Training

Members of Ukraine's Territorial Defense Forces, volunteer military units of the Armed Forces, train in a city park in Kyiv, Ukraine. (AP/Efrem Lukatsky)

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The U.S. military depends on a constellation of GPS satellites to guide precision bombs from its jets down to the target. These communications links are now in danger of being severed, Hodges said. 

Asked about Putin’s motivations for moving over 100,000 troops to Ukraine’s border and thousands more offshore in the Black Sea and Sea of Azov, Hodges said, "I think he assumed that we would have already blinked by now, that we would have rolled over on some of the outrageous demands that the Kremlin made." 

Asked how any potential Russian military operations would commence in Ukraine, Hodges said, "They will be using cyber. They will be using sabotage. They will be using disinformation to create havoc and confuse us, but I just don't think they have the capability to capture Kyiv," the capital city. 

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In addition to NATO, there is something else that Putin fears the most, Hodges said. 

"He sees the idea of a Ukraine that begins to look like Poland or Estonia in terms of freedom and prosperity on his border. That's a real danger for him, because in Russia people are going to say, ‘Well, why don't we have that? Why is our life so bad compared to how it is in Ukraine?’ That's the danger he’s concerned about." 

Fox News’ Melissa Chrise contributed reporting from Kyiv, Ukraine.