The US has confirmed it will provide Ukraine with the key Patriot missile defence system to help its fight against Russia.
Patriot missile systems essentially act as a shield against incoming jets, short-range ballistic missiles and cruise missiles.
The transfer is a significant step for the Ukrainian defence and will be the first-ever handover of such a system to Ukraine, but one expert claimed it will make only a "minor difference to the number of missiles that will get through the Ukrainian's air defence."
Biden's administration had previously been reluctant, in part due to a possible response from Russia, to supply the system.
However, Russian missiles have caused repeated problems such as power outages and it is hoped the new systems will help Ukraine improve its air cover.
On Wednesday, the White House confirmed the Patriot would be part of another $1.85 billion (£1.53 billion) in aid.
Also included in the package are mortars, military vehicles, ammunition for the High Mobility Artillery Rocket Systems (HIMARS), artillery and small arms.
The move comes as Ukrainian President Volodymyr Zelensky visits the US today in a landmark visit to shore up the military ties between the two nations.
Security expert Dr Rod Thornton of the Defence Studies Department at King's College London told the Mirror the system will help Ukraine, "especially against the more advanced missiles the Russians are firing."
The US package included just one Patriot battery, which has eight launchers each with a capacity of four missile interceptors.
Patriots also come with ground radar and a control station.
He said: "Those kind of really effective, strategic level missiles, will be more easily intercepted by a Patriot missile system."
One of the drawbacks the system has is that it is extremely expensive, with missiles costing around $4 million (£3.3 million) a round.
Part of Russia's cheaper air attack is the drones it has purchased from Iran, which costs somewhere in the region of $50,000 (£41,000).
Thornton added: "Will it stop the hundreds of Iranian drones? I mean, there is no point in firing a very expensive Patriot missile at a very small Iranian drone. Those drones will still get through the Ukrainian air defence system."
Biden has previously ruled out sending Patriots to Ukraine, but there are suggestions the change in policy may have come as Vladimir Putin's forces continue to focus strikes on Ukraine’s civilian infrastructure.
Russia has previously warned a missile system like the Patriot would be "another provocative move by the US."
In response to a question about possible escalation, Biden said: "It’s not escalatory, it’s defensive,” Mr Biden said, adding, “We’d love to have them not use it. Just stop the attacks."
Thorton, sceptical of the difference the Patriot will make, said the US may have changed its tune as something "had to be done" to protect critical national infrastructure (CNI) over a cold winter.
"If more CNI is hit," he said. "Then what does that mean in terms of deaths from cold in Ukrainian cities?
"So, something had to be done and I think there was pressure in America for the administration to supply the Patriot."
Biden said: "Russia is using winter as a weapon. Freezing people. Starving people. Cutting them off from one another. It’s the latest example of the outrageous atrocities Russian forces are using."
Another barrier to the proposal was that the batteries can require up to 90 troops to operate it.
Biden confirmed that Ukrainian troops will have to be trained how to use the structure.
"I don't think they are going to supply that many because they need them themselves," Thornton added.
Thornton believes "the Patriot will not make that much difference" at first, due to the time taken to train troops.
US Secretary of State Antony Blinken said in a statement: "Today's assistance for the first time includes the Patriot Air Defense System, capable of bringing down cruise missiles, short-range ballistic missiles, and aircraft at a significantly higher ceiling than previously provided air defence systems."
