The US House of Representatives approved the package on Saturday after months of delays by some Republicans wary of US involvement overseas. It was passed by the US Senate on Tuesday, and US President Joe Biden said he would sign it on Wednesday.

The difference could be felt within days on the front line in eastern and southern Ukraine, where Russia’s much larger army has been slowly taking territory against massively outgunned Ukrainian forces.

The aid approval means Ukraine may be able to release artillery ammunition from dwindling stocks that it has been rationing. More equipment will come soon from American stocks in Poland and Germany, and later from the US.

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The first shipments are expected to arrive by the beginning of next week, said Davyd Arakhamia, a lawmaker with Ukrainian President Volodymyr Zelensky’s Servant of the People party.

But opposition lawmaker Vadym Ivchenko, a member of the Ukrainian parliament’s National Security, Defence and Intelligence Committee, said logistical challenges and bureaucracy could delay shipments to Ukraine by two to three months, and it would be even longer before they reach the front line.

While details of the shipments are classified, Ukraine’s most urgent needs are artillery shells to stop Russian troops from advancing, and anti-aircraft missiles to protect people and infrastructure from missiles, drones and bombs.

What’s coming first is not always what front-line commanders need most, said Arakhamia, the Ukrainian lawmaker. He said that even a military giant like the US does not have stockpiles of everything.

“The logic behind this first package was, you (the US) finds our top priorities and then you see what you have in the warehouses,” Arakhamia said. “And sometimes they do not match.”

Hope for future breakthroughs for Ukraine still hangs on more timely deliveries of Western aid, lawmakers acknowledge.

Many experts believe that both Ukraine and Russia are exhausted by two years of war and won’t be able to mount a major offensive – one capable of making big strategic gains – until next year.

Still, Russia is pushing forward at several points along the 1,000km (600-mile) front, using tanks, wave after wave of infantry troops and satellite-guided gliding bombs to pummel Ukrainian forces.

Russia is also hitting power plants and pounding Ukraine’s second-largest city, Kharkiv, which is only about 30km from the Russian border.

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Ivchenko said the goal for Ukraine’s forces now is to “hold the line” until the bulk of new supplies arrive by midsummer. Then, they can focus on trying to recapture territory recently lost in the Donetsk region.

“And probably … at the end of summer we’ll see some movement, offensive movement of the Ukrainian armed forces,” he said.

Some military experts doubt Ukraine has the resources to mount even small offensives very soon.

The US funding “can probably only help stabilise the Ukrainian position for this year and begin preparations for operations in 2025,” said Matthew Savill, director of military sciences at the Royal United Services Institute, a think tank.

In the best-case scenario for Ukraine, the American aid will give commanders time to reorganise and train its army – applying lessons learned from its failed summer 2023 offensive. It may also galvanise Ukraine’s allies in Europe to increase aid.

Zelensky insists Ukraine’s war aim is to recapture all its territory from Russia – including Crimea, seized illegally in 2014. Even if the war ultimately ends through negotiation, as many experts believe, Ukraine wants to do that from as strong a position as possible.

Whatever happens on the battlefield, Ukraine still faces variables beyond its control.

Former US president Donald Trump, who seeks to retake the White House in the November election, has said he would end the war within days of taking office.

And the 27-nation Europe Union includes leaders like Hungarian President Viktor Orban and Slovakian Prime Minister Richard Fico, who have opposed arming Ukraine.

Ukraine’s allies have held back from supplying some arms out of concern about escalation or depleting their own stocks. Ukraine says that to win the war it needs longer-range missiles it could use for potentially game-changing operations such as cutting off occupied Crimea, where’s Russia’s Black Sea fleet is based.

It wants Army Tactical Missile Systems, known as ATACMS, from the US and Taurus cruise missiles from Germany. Both governments have resisted calls to send them because they are capable of striking targets deep within Russian territory.

The new bill authorises the US president to send Ukraine ATACMS “as soon as practicable”. It’s unclear what that will mean in practice.

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Sometimes, promised weapons have arrived late, or not at all. Zelensky recently pointed out that Ukraine is still waiting for the F-16 fighter jets it was promised a year ago.

Meanwhile, Russia is using its advantage in troops and weapons to push back Ukrainian forces, perhaps seeking to make maximum gains before Ukraine’s new supplies arrive.

For weeks it has pummelled the small eastern city of Chasiv Yar, at the cost of 900 soldiers killed and wounded a day, according to the UK Ministry of Defence.

Capturing the strategically important hill town would allow them to move toward Sloviansk and Kramatorsk, key cities Ukraine controls in the eastern region of Donetsk.

It would be a significant win for Russian President Vladimir Putin, who Western officials say is bent on toppling Ukraine’s pro-Western government.