The EU has earmarked €450 million ($503 million) for lethal arms, which include air-defense systems, anti-tank weapons, ammunition, and other military equipment for Ukraine's armed forces. A further €50 million will be spent on providing non-lethal supplies such as fuel, protective gear, helmets, and first-aid kits.

As EU treaties do not allow it to tap into its normal budget for military purposes, the bloc is activating a vehicle called the European Peace Facility, which allows it to provide military aid up to a ceiling of €5 billion.

It comes after a paradigm shift in Germany's defense policy, which saw it sign off on providing lethal weapons to Ukraine, including 1,000 anti-tank weapons and 500 "Stinger" class surface-to-air missiles, thereby reversing its ban on supplying lethal weapons to a war zone.

The US is also stepping up its shipments and providing an additional $350 million (€313 million) in military assistance, including Javelin antitank missiles, Stinger anti-aircraft missiles, small arms and ammunition.

That brings the total of US military aid to Ukraine to $1 billion over the past year and to more than $2.5 billion since 2014.

The logistical challenges

While this signals a huge boost for Ukraine in its effort to repel Russian forces, there are concerns about the logistics involved and the potential obstacles. Questions surround the timing and the routes.

So far, military aid from the West has been delivered by land or air, depending on the type of weapon.

But the airspace over Ukraine is now controlled by Russian fighter jets that could intercept the shipments "predominantly by airstrikes and missile strikes. If they know the routes they can take them under surveillance and look for the specific means of transportation," Gustav Gressel, an expert on Eastern Europe and defense policy with the European Council on Foreign Relations think tank, told DW via email.

The prospect of such a disruption puts the spotlight on Poland, which shares a 535-kilometer (332-mile) long border with Ukraine. The US Army, in particular, has a long history of dispatching forces and equipment through Poland.

And the onus on Poland is increasing following Hungary's refusal to allow lethal arms to transit its territory.

Poland's role

"All of this equipment is basically massing on the Polish border at the moment. Even if Slovakia, for example, wanted to, it's not an easy route because of the geography of the mountain ranges that move from Slovakia down through Romania. So there are two routes: One is close to the Belarusian border, then there's one slightly south," Ed Arnold, a research fellow for European Security at the Royal United Services Institute, a London-based think tank, told DW.

Marc Finaud, head of Arms Proliferation at the Geneva Center for Security Policy, notes that the dynamics on the ground could shift very quickly. "If these convoys or transports would be stopped — if Western countries are under attack, whether they are within NATO or already across the border into Ukraine — that could increase the tensions and the escalation," he told DW.

Arnold says the danger of such an escalation is currently holding back the Russians because "you would be targeting Western resupply."

Still, he says he's surprised that they haven't cut it off "because actually that would useful for their strategy if they could take those two routes. The Russians have the option of moving from the south-west of Belarus and interdicting all of this equipment that's coming in."

Time is of the essence

The other crucial factor is time, which is running out fast for reinforcements to get to Ukrainian forces in Kyiv and Kharkiv.

This, says Arnold, is particularly problematic for "the Ukrainian forces on the eastern line of contact who are potentially going to be cut off if they don't move to the west of the Dnieper River soon. They will need to resupply because they're doing the heaviest fighting and they are the best Ukrainian troops from the 95th Air Assault Brigade."

So is there any other way to get the western arms systems to the front lines in Ukraine? "The other possibility is that Ukrainian or foreign fighters could pick things up in Poland and then move over the border, but that's not in great numbers," said Arnold.

At this stage the danger of ammunition supplies drying up is critical, says Arnold. "There's maybe five days left of ammo for the heavier systems the Ukrainians have. The other option they have is to capture Russian abandoned weapons, which will sustain them for a little while, but not a huge amount of time."

Edited by: Jane Paulick