(NewsNation) — Western weaponry in Ukraine helped block Russia’s offensive thus far, but the fight is ramping up as it heads to the eastern Donbas region.

The majority of Ukraine’s weapons came from the United States. These include more than 12,000 weapons designed to defeat armored vehicles, some 1,400 shoulder-fired Stinger missiles to shoot down aircraft and more than 50 million rounds of ammunition, among many other things. Dozens of other nations are adding to the totals.

The White House announced it will provide an additional $800 million in weapons, ammunition and other security assistance to Ukraine. After speaking with Ukrainian leader Volodymyr Zelenskyy Tuesday, U.S. President Joe Biden said the new package of assistance will contain “many of the highly effective weapons systems” his administration has already provided to Ukraine, along with new capabilities. These capabilities, which include artillery systems, artillery rounds and armored personnel carriers, are tailored to the wider assault the White House expects Russia to launch in eastern Ukraine.

The presidents of Poland, Lithuania, Latvia and Estonia, all NATO countries, traveled by train Wednesday to Kyiv to meet Zelenskyy.

Finland and Sweden also took steps toward joining NATO on Wednesday. Finland will take a formal vote in the coming weeks on whether or not it will join NATO. Russia has warned both countries against joining the alliance.

This comes as Russia said troops from the Ukrainian 36th Marine Brigade surrendered in the besieged southeastern port of Mariupol. Ukraine has denied Russia’s claim, according the Associated Press.

Ukraine appears to have new leverage in the fight after detaining oligarch Viktor Medvedchuk, a close ally of Russian President Vladimir Putin. In February, Kyiv said Medvedchuk, the leader of the Opposition Platform — For Life party, had escaped from house arrest. Last year, authorities opened a treason case against Medvedchuk, who denies wrongdoing. 

Called “the dark prince” of Ukrainian politics, according to The Guardian, Medvedchuk has been a loyal ally to Putin for over two decades.

As The Guardian reports, their ties are deeper than politics or business— Putin is the godfather of Medvedchuk’s daughter and the two have taken vacations together.

Zelenskyy said Tuesday his operatives had “conducted a lightning-fast and dangerous multilevel special operation” to arrest Medvedchuk, but did not give details. He’s hoping to do a prisoner swap with Putin to end the war.

U.S. officials and analysts offer numerous explanations for why the Russians have had so little success interdicting Western arms moving overland from neighboring countries, including Poland. Among the likely reasons: Russia’s failure to win full control of Ukraine’s skies has limited its use of airpower. Also, the Russians have struggled to deliver weapons and supplies to their own troops in Ukraine.

Some say Moscow’s problems begin at home.

“The Russians have to find the needle in this very big haystack to destroy the weapons and ammo they’re after and not waste scarce munitions on trucks full of printer paper or baby diapers or who knows what,” said Stephen Biddle, a professor of international and public affairs at Columbia University.

Even with this Western assistance, it’s uncertain whether Ukraine will ultimately prevail against Russian forces. While Russian troops have withdrawn from the Kyiv area, Ukrainians in these places have continued to unearth new horrors. In the village of Yahidne, which is 87 miles from Kyiv, Russian soldiers forced more than 300 people into a school basement at gunpoint. During weeks of stress and deprivation, some began to die.

As the fighting intensifies in the Donbas and perhaps along the coastal corridor to the Russian-annexed Crimean Peninsula, Putin may feel compelled to strike harder at the arms pipeline, which Zelenskyy has called vital to his nation’s survival.

In the meantime, a staggering volume and range of war material is arriving almost daily.

“The scope and speed of our support to meeting Ukraine’s defense needs are unprecedented in modern times,” said John Kirby, the Pentagon press secretary. He said the approximately $2.5 billion in weapons and other material that has been offered to Ukraine since the beginning of the Biden administration is equivalent to more than half of Ukraine’s normal defense budget.

The specific routes used to move the U.S. and other Western materials into Ukraine are secret for security reasons, but the basic process is not. Just this week, two U.S. military cargo planes arrived in Eastern Europe with items ranging from machine guns and small arms ammunition to body armor and grenades, the Pentagon said.

A similar load is due later this week to complete the delivery of $800 million in assistance approved by President Joe Biden just one month ago. The weapons and equipment are offloaded, moved onto trucks and driven into Ukraine by Ukrainian soldiers for delivery.