The U.S. Navy Arleigh Burke-class guided-missile destroyer USS Porter sails in formation during the multinational maritime…
FILE - The U.S. Navy Arleigh Burke-class guided-missile destroyer USS Porter sails in formation during the multinational maritime exercise Sea Breeze 2020, co-hosted by Ukraine and the United States, in the Black Sea, July 25, 2020.

When it comes to the Black Sea, international attention has been focused for weeks on the opulent $1.37 billion mansion jailed Kremlin critic Alexei Navalny says is owned by Russian President Vladimir Putin.  

Tagged "Putin's Palace" by the Russian leader's foes, the 1,800-square-meter mansion is located on the Black Sea's northeastern shore near the Soviet-era resort town of Gelendzhik, once an outpost for 19th-century slave trading between the Caucasus and the Ottoman Empire. 

It is also a good spot to observe Black Sea naval maneuvers, of which in the past few days there have been plenty.  

The U.S. Navy, along with NATO partners, has dramatically increased a maritime presence in the Black Sea, part of a strategy to emphasize that Russian militarization of the waters between Europe and Asia since the 2014 annexation of Crimea will not go unchallenged. 

FILE - U.S. Navy guided-missile destroyer USS Porter sails in the Bosphorus, on its way to the Black Sea, in Istanbul, Turkey, Jan. 28, 2021.

Last week, the USS Porter, a guided missile destroyer, entered the waters to join the USS Donald Cook and a refueling ship, the USNS Laramie, in the largest deployment of the U.S. Navy in the Black Sea since 2017.  

The three ships are patrolling alongside other NATO and Ukrainian warships and taking part in naval exercises that were postponed last year because of the coronavirus pandemic.

A NATO spokesman said the Western alliance was boosting its Black Sea presence "in response to Russia's illegal and illegitimate annexation of Crimea from Ukraine and its ongoing military buildup."  

In the five years since Moscow annexed the Ukrainian peninsula, Russia has turned the Black Sea region into a "military fortress," say Western officials and independent military analysts, boosting military personnel on the ground and developing air, naval and coastal defense systems. 

"The ongoing and accelerated militarization of the Crimean Peninsula and its surrounding waters has in fact created a new security reality in the Black Sea and the wider Mediterranean region," Ukrainian envoy Yevhenii Tsymbaliuk told a January 14 meeting of the Organization for Security and Co-operation in Europe.  

FILE - The Russian Navy's frigate Admiral Makarov sets sail in the Bosphorus, on its way to the Mediterranean Sea, in Istanbul, Turkey, Feb. 28, 2020.

Russia has responded to the Western exercises, dispatching a Bastion missile defense system to Crimea and deploying the Admiral Makarov frigate, which has already tried to disrupt NATO training maneuvers by locking onto air targets and jamming electronic communications, according to Western officials.  

On Sunday, a Russian warplane aggressively buzzed the USS Donald Cook, according to U.S. military officials. The Russian Sukhoi Su-24 jet got as close as 91 meters off the ship's port beam, according to Cmdr. Kyle Raines, a spokesman for the U.S. 6th Fleet. 

Ahead of the U.S. naval deployment, President Joe Biden warned Moscow that he would "act firmly" against Russian aggression in the region. 

The Black Sea region "matters to the West and to the Kremlin," said retired Lt. Gen. Ben Hodges in a paper published last week by the Center for European Policy Analysis, a defense think tank in Washington.  

Hodges, who retired in 2018 after serving for three years as commanding general of U.S. Army Europe, said U.S. and Western strategy in the region has been insufficient and argues that great-power competition can prevent great-power conflict.  

"Conversely, failure to compete and to demonstrate and protect interests, in all domains, can lead to power vacuums and misunderstandings that can, in turn, lead to an escalation of tensions and actual conflict," he wrote. 

Hodges and other Western analysts acknowledge that the Kremlin wants to prevent the Black Sea from becoming a "NATO lake" but aims to ensure that no new East-West energy corridor can bypass Russia or weaken its grip on oil and gas exports.  

But Moscow has become increasingly aggressive, exploiting regional conflicts in Georgia and Transnistria, and seizing the Ukrainian Black Sea peninsula of Crimea to boost its military presence and advance dominance in the region. 

The Russian military has also been using the Black Sea for naval operations in the Eastern Mediterranean in support of Syrian President Bashar al-Assad and to assist the warlord Gen. Khalifa Haftar in Libya, military observers say.  

FILE - Russian armored personnel carriers submerge from amphibious assault ships during the Navy Day parade in the Black Sea port of Sevastopol, Crimea, July 26, 2020.

Russian naval forces have also been accused of seeking to close the neighboring Sea of Azov to Ukrainian cargo vessels, disrupting unimpeded access and breaching a 2003 maritime treaty between Moscow and Kyiv. 

In November 2018, Russia seized three Ukrainian naval vessels in the strait, holding their 24 seafarers until a controversial swap eight months later that saw Kyiv hand over five riot police officers accused of killing protesters during the 2014 Maidan uprising. 

The annexation of Crimea means Russia now shares direct maritime borders not only with NATO member Turkey but also with Bulgaria and Romania, two other alliance members.

Speaking at Britain's Chatham House in 2019, Col. Vadym Skibitskyi, deputy director of Ukraine's defense intelligence agency, said all Black Sea countries should be worried about Russia's military buildup.  

He noted that before the 2014 annexation, Russia had 22 combat aircraft in the region but now has 122, and has boosted its submarine tally from two to seven and warships from 22 to a planned 45 next year. 

His biggest fear, he said, was of "a maritime blockade of Ukraine."