KHARKIV, UKRAINE -- The table tennis coach, the chaplain's wife, the dentist and the firebrand nationalist have little in common except a desire to defend their hometown and a sometimes halting effort to speak Ukrainian instead of Russian.

The situation in Kharkiv, just 40 kilometres from some of the tens of thousands of Russian troops massed at the border of Ukraine, feels particularly perilous. Ukraine's second-largest city is one of its industrial centres and includes two factories that restore old Soviet-era tanks or build new ones.

It's also a city of fractures: between Ukrainian speakers and those who stick with the Russian that dominated until recently; between those who enthusiastically volunteer to resist a Russian offensive and those who just want to live their lives. Which side wins out in Kharkiv could well determine the fate of Ukraine.

If Russia invades, some of Kharkiv's 1 million plus people say they stand ready to abandon their civilian lives and wage a guerrilla campaign against one of the world's greatest military powers. They expect many Ukrainians will do the same.

"This city has to be protected," said Viktoria Balesina, who teaches table tennis to teenagers and dyes her cropped hair deep purple at the crown. "We need to do something, not to panic and fall on our knees. We do not want this."

Balesina recalls being pressured to attend pro-Russia rallies during the protest movement that swept Ukraine after Russia attacked in 2014 -- a year that utterly changed her life. A lifelong Russian speaker born and raised in Kharkiv, she switched to Ukrainian. Then she joined a group of a dozen or so women who meet weekly in an office building for community defence instruction.

Now her Ukrainian is near-fluent, though she still periodically grasps at words, and she can reload a sub-machine gun almost comfortably.

This wasn't the life she expected at age 55, but she's accepted it as necessary. Plenty of people in her social circle sympathize with Russia, but they're not what drives her today.

"I am going to protect the city not for those people but for the women I'm training with," she said.

Among her group is Svetlana Putilina, whose husband is a Muslim chaplain in the Ukrainian military. With grim determination and not a hint of panic, the 50-year-old has orchestrated emergency plans for her family and for her unit: Who will take the children to safety outside the city? Who will accompany elderly parents and grandparents to one of the hundreds of mapped bomb shelters? How will the resistance women deploy?

"If it is possible and our government gives out weapons, we will take them and defend our city," said the mother of three and grandmother of three more. If not, she at least has one of her husband's service weapons at home, and she now knows how to use it.

Elsewhere in Kharkiv, Dr. Oleksandr Dikalo dragged two creaky exam chairs into a labyrinthine basement and refilled yellow jerrycans with fresh water. The public dental clinic he runs is on the ground floor of a 16-story apartment building, and the warren of underground rooms is listed as an emergency shelter for the hundreds of residents.

Dikalo knows how to handle weapons as well, from his days as a soldier in the Soviet Army when he was stationed in East Germany. His wife works as a doctor at Kharkiv's emergency hospital and regularly tends to Ukrainian soldiers wounded at the front.

The conflict that began in Ukraine's Donbas region subsided into low-level trench warfare after agreements brokered by France and Germany. Most of the estimated 14,000 dead were killed in 2014 and 2015, but every month brings new casualties.

"If God forbid something happens, we must stand and protect our city. We must stand hand to hand against the aggressor," Dikalo said. At 60 he's too old to join the civil defence units forming across the country, but he's ready to act to keep Kharkiv from falling.

A guerrilla war fought by dentists, coaches and housewives defending a hometown of a thousand basement shelters would be a nightmare for Russian military planners, according to both analysts and U.S. intelligence officials.

"The Russians want to destroy Ukraine's combat forces. They don't want to be in a position where they have to occupy ground, where they have to deal with civilians, where they have to deal with an insurgency," said James Sherr, an analyst of Russian military strategy who testified last week before a British parliamentary committee.

There are growing calls in Washington for the CIA and the Pentagon to support a potential Ukrainian insurgency. While Russia's forces are larger and more powerful than Ukraine's, an insurgency supported by U.S.-funded arms and training could deter a full-scale invasion.

Polling of ordinary Ukrainians reviewed by intelligence agencies has strongly indicated there would be an active resistance in the event of an invasion, according to two people familiar with the matter who spoke on condition of anonymity to discuss sensitive information. A spokesperson for the U.S. Director of National Intelligence declined to comment.

Russia denies having plans for an offensive, but it demands promises from NATO to keep Ukraine out of the alliance, halt the deployment of NATO weapons near Russian borders and to roll back NATO forces from Eastern Europe. NATO and the U.S. call those demands impossible.

Ukrainian President Volodymyr Zelenskyy said recently that any escalation could hinge on Kharkiv. The city is also the base for Yevheniy Murayev, identified by British intelligence as the person Russia was considering installing as president.

"Kharkiv has over 1 million citizens," Zelenskyy told The Washington Post. "It's not going to be just an occupation; it's going to be the beginning of a large-scale war."

That is precisely what Anton Dotsenko fears. At 18, he was front and centre in the wave of protests that brought down the pro-Russia government in 2014. Now he's a 24-year-old tech worker, and he's had enough upheaval.

"When people are calm and prosperous, and everything is fine, they don't dance very well. But when everything's bad, that's when they party hard, like it's the last time," Dotsenko said during a smoke break outside a pulsing Kharkiv nightclub. "This is a stupid war, and I think this could all be resolved diplomatically. The last thing I would like to do is give my life, to give my valuable life, for something pointless."

The young people dancing inside would say the same, he declared in Russian: "If the war starts, everyone will run away."

This is what one nationalist youth group hopes to prevent. They meet weekly in an abandoned construction site, masked and clad in black as they practice maneuvers. The men who join that group or the government-run units have already shown themselves to be up for the challenge to come, said one of the trainers, who identified himself by the nom de guerre Pulsar.

"Kharkiv is my home and as a native the most important city for me to protect. Kharkiv is also a front-line city, which is economically and strategically important," he said, adding that many people in the city are "ready to protect their own until the end," as are many Ukrainians.

The same sentiment rings out among Ukrainians in the capital, Kyiv, and in the far west, in Lviv.

"Both our generation and our children are ready to defend themselves. This will not be an easy war," said Maryna Tseluiko, a 40-year-old baker who signed up as a reservist with her 18-year-old daughter in Kyiv. "Ukrainians have a rich tradition of guerrilla warfare. We don't want to fight Russians. It's the Russians who are fighting us."

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Lori Hinnant reported from Paris. Associated Press writers Yuras Karmanau in Kyiv, and Nomaan Merchant in Washington, contributed to this report.