Kyiv — All of Ukraine was put under an air raid alert Monday morning as Vladimir Putin's military stepped up attacks on the day when the world marks the defeat of Nazi Germany in World War II. Ukrainian President Volodymyr Zelenskyy marked Victory in Europe Day with a vow that "all the old evil that modern Russia is bringing back will be defeated, just as Nazism was defeated."

As he did so, the mayor of Kyiv said Ukraine's capital had come under the most intense aerial assault since the start of Russia's full-scale invasion in February 2022.

Tracer fire streaked across Kyiv's skyline overnight before a loud bang, as Ukraine's air defenses scored a direct hit, intercepting an incoming Russian explosive drone. Authorities said a few people were wounded by falling shrapnel, but there were no immediate reports of deaths from the attack on Kyiv. 

Authorities said every one of the 35 Iranian-made drones flown at Kyiv overnight was intercepted.

With its ground war largely stalled amid apparent ammunition shortages and internal divisions, Russia has gone on the attack ahead of Ukraine's long-anticipated spring counteroffensive, unleashing missiles on cities across the country for more than a week, including the latest barrage overnight.

Little more than one year ago, few people believed Ukraine's vastly outnumbered forces would manage to hold out for even a month against Russia.

But now, the army of underdogs — bolstered by billions of dollars worth of military hardware from the U.S. and other partners — is gearing up for a battle that could prove pivotal in the course of the war.

Training at a quarry 15 miles from the front line, CBS News met new Ukrainian recruits who, despite a complete lack of military experience, were being trained on every weapon in the country's arsenal, for whatever the next battle may bring.

One soldier at the training ground, callsign "Spartacus," has been fighting the Russians since the first invaded his country in 2014.

He said he was training the recruits on both old Soviet weapons and modern U.S. and European-made equipment.

"Zhuk," a high school history teacher who was training for the new chapter in his life as a soldier, told CBS News his goal was to "come back home with the victory, soon."

He said he was eager for himself and his fellow Ukrainians to be able to "return to the normal life that we all have lost."

In Russia, authorities were preparing for their annual "Victory Day" celebrations on Tuesday. But this year's events, which celebrate the then-Soviet Union's vital role in helping defeat Nazi Germany, were being scaled-back, with Russian officials warning of the threat of Ukrainian attacks.

As both sides prepare for the battle ahead, Ukraine's troops are determined to win this war before the end of the year. Whatever victory looks like.

In:
• War
• World War II
• Ukraine
• Russia
• Adolf Hitler
• War Crimes
• Vladimir Putin
• Nazi