From the first hours of Russia’s invasion of Ukraine, the famous port city of Odesa has largely been without a working port. Once bustling with cargo vessels, cruise ships, sailboats, yachts and fishing trawlers, the harbor is now a vast expanse of open water.

Sophia Dobrovolska, a 16-year-old aspiring merchant marine at the Odesa Sea Academy, lives on that empty sea. And her dreams of sailing out into the wider world from Odesa remain thwarted as long as Russian warships command the coast, mines line the waterways and nearly all movement of civilian ships remains forbidden.

“I was born and lived all of my life in Odesa,” she said. “When the full-scale war started, my mom thought of leaving, but I told her: ‘No, my college is here. I will not go.’”

President Vladimir V. Putin of Russia has ​long made clear that he wants to capture Odesa, a goal that looks increasingly less likely. This summer, his forces began bombarding the ports that helped shape the city’s rich multinational, multilingual and multiethnic history, which is reflected in the tapestry of architectural styles found across the city. Some of those gems are now in ruins.

Although Russia did not take Odesa, it did gain control of the Black Sea and has effectively blockaded Ukrainian ports, crippling the economy and threatening global food supplies.

But in recent weeks, Ukraine’s military campaign to reclaim the sea has gathered pace.

Ukrainian special forces have driven the Russians from several drilling platforms in the waters between Crimea and Odesa, undercutting Russia’s ability to project power off the Ukrainian coast — so long as Ukraine can maintain control of the platforms. And after taking out several important Russian air-defense systems on Crimea, Ukrainian missiles struck a Russian submarine and a large landing ship at the fleet’s largest dry dock on the occupied peninsula.

On Friday, the Ukrainians struck a major Russian naval command post on Crimea before hitting the main headquarters building of the Russian Black Sea Fleet in the occupied city of Sevastopol. Ukraine’s military asserted on Monday that it had killed the commander of Russia’s Black Sea Fleet in that strike, a claim that has not been independently verified. If true, that would be a major blow to Russia.

In addition, in recent days, the first cargo container ships set off from Odesa since July — when Russia pulled out of an internationally brokered deal that allowed millions of tons of grain and ore to be exported from the city’s ports.

Although Russia did not stop the ships, on Monday it hit Odesa’s ports with yet another large-scale missile and drone barrage. The attack inflicted significant damage on grain infrastructure, a hotel and a seaport. The Ukrainian department of defense said the strikes were a “pathetic attempt at retaliation.”

As the fighting intensifies, the disconnect between this city and the sea, which is never much more than a 15-minute walk from any quarter, feels foreboding and strange.

In the moonlight on a clear night in late summer, instead of the lights atop ship masts bouncing like shimmering stars where the sea meets the sky, there were distant flashes of yellow. It was not lightning, locals said, but most likely missiles fired from Russian warships taking aim at Ukrainian cities.

Vadym Zakharchenko, the vice rector of the National University of the Odesa Maritime Academy and a lifelong Odesan, said every time he goes to the beach, he is struck by the absence of ships.

“I told my wife: ‘Look. How is it possible to have such a situation?’” he said.

Andriy Cheban, the deputy director of the Navigation College at the Odesa Sea Academy, a college that is a part of the National University of the Odesa Maritime Academy, said he felt a “silent hatred” for the “pirates” who have cut Odesa off from the sea.

“The enemy deprived us of the opportunity to work,” he said. “And Ukraine has some of the best sailors in the world.”

Still, he is confident his students will not be without their sea forever.

As the war slogs on, Sophia — like millions of young people across Ukraine — is trying to plan for the future while worrying about surviving the present.

She said her goal had been to one day be the captain of a mighty trade ship. That would make her part of Odesa’s rich history of seafaring, and Ukraine’s outsize role in the world’s shipping industry. There are some 80,000 Ukrainian sailors in nearly every port on the planet, according to Evheniy Ignatenko, the head of maritime administration, and Ukrainians account for some 15 percent of ship officers around the world, according to one industry estimate from before the war began.

Her ambitions have changed, though.

“Now, as we are at war, I also think that I would like to be part of the Navy and help my country,” she said.

As Sophia walked with her mother on the shore one morning, loud explosions rumbled in the distance. The Russians were bombarding Snake Island, a tiny patch of 46 acres of rock and grass about 75 miles from Odesa.

Ukraine drove the Russians from Snake Island over a year ago, a critical first step in the battle to keep Russia from turning Ukraine into a landlocked rump state.

Sophia is one of 7,000 students at the sea academy. An undisclosed number of cadets also attend the affiliated military Naval Institute in the city.

Dressed in their crisp blue-and-white uniforms and seen at coffee shops, hopping on trolleys, and walking the streets as they head to classes, the cadets are a constant reminder of both what Ukraine has lost and its defiant hope for the future.

Many of the cadets come from seafaring families and are the third, fourth or even fifth generation to take on the trade. Sophia’s love of the sea came from watching her aunt work at the harbor. She always liked watching her around the big ships, she said.

“And I love the way the water changes color,” Sophia said.

The waters of the Black Sea, one of the four seas named in English after common colors, acquire a wide range of hues depending on the conditions. Viewed from space, they are milky blue near the coast, while turquoise swirls stretch off into the distance.

“It is so sad that we cannot go to our sea,” Sophia said as she looked at the maps and chart in a classroom designed to simulate a ship’s navigation station.

Cadets are taught how to avoid collisions when winds blow hard, fog hangs heavy and storms rage. But there is no chart to help map a course through the tempest of war.

“Sometimes it’s really scary,” Sophia said. “I can hear the rockets as they fly above my house and then are shot by our air defense.”

The first lesson for the aspiring merchant marines is not about seafaring, but instead about where to seek shelter during an air raid.

But even an empty sea, she said, can bring a sense of calm.

“The sea has always been a source of peace and beauty for me,” she said.

She does not know how long it will take for the war to end, but when it does, she said, she will be ready and free to once again be the captain of her own destiny.

Anna Lukinova contributed reporting from Odesa.