The US has authorised western allies to give F-16 fighter jets to Ukraine – and endorsed the training of Ukrainian pilots to fly the warplanes.
The move by US President Joe Biden was welcomed by the UK, Netherlands, Belgium and Denmark.
On Friday, Prime Minister Rishi Sunak tweeted: “The UK will work together with the USA and the Netherlands, Belgium and Denmark to get Ukraine the combat air capability it needs. We stand united.”
But how many jets will be delivered, when and which countries will provide them?
Here Sky News takes a closer look at the F-16 fighter jets and their significance for Ukraine’s war efforts.
Why would F-16s be so important for the war?
Ukraine has gained confidence with the West providing more support and longer-range weapons. However, at the moment, Mr Bell said Zelenskyy has been asking for the capability for the past year, adding “fighter aircraft are the one thing that he can’t match Russia with.”
He adds that if the West provides manned combat aircraft, then the Russian air force “most certainly wouldn’t stand a chance.”
The F-16s hold significance in supporting Ukrainians in the war, but Mr Bell says it might take months or even years for military troops to learn how to operate the aircraft.
“This is about giving capability. And Zelenskyy has been banging the drum up until now.
“The West has been reluctant to do that because they know it will take time, but it would prove a very decisive capability in this conflict.”
What are the F-16s?
The F-16 is built by the American defence contractor Lockheed Martin.
It is a multi-role fighter aircraft created for the United States Air Force.
The F-16 has an internal M61 Vulcan cannon and 11 locations for mounting weapons and other equipment.
Its payload typically consists of two 2,000lb (907kg) bombs, two AIM-9 Sidewinder short-range air-to-air missiles, two AIM-120 medium-range air-to-air missiles and two 2,400lb (1,088kg) external fuel tanks.
The jet can travel at speeds up to 1,500mph and has a range of more than 2,002 miles.
It has a wingspan of 32ft 8in (9.9m) and a length of 49ft 5in (13.8m). It weighs 19,700lb (8,935kg) without fuel and has a maximum takeoff weight of 37,500lb (17,010kg).
There is both a single-seat and two-seat model of the aircraft.
In 1991, during the Gulf War, F-16s were used to attack airfields, military production facilities and other targets.
It has also been used and flown in American conflicts in Afghanistan, Iraq, Kosovo and the Persian Gulf.
They are operated by several countries other than the US, including Poland, Belgium, the Netherlands, and Denmark.
When can F-16s be realistically delivered?
There are two key factors to think about.
As F-16s are produced by the US, the Americans would need to provide permission to other nations to give their F-16 aircraft.
“The second thing is F-16s are the most widely exported aircraft in the world as there are a lot of them about,” Bell adds.
There are two factors to consider for the F-16s plan to fall into place.
First, training must take place to ensure pilots can fly the aircraft.
And second, it’s important to think about how the F-16s will actually be delivered.
Bell added: “Although there’s lots of countries operating them because it’s so expensive, nobody has more aircraft than they need, and nobody could afford to give to 20 to 30 of these platforms to Ukraine.”
Which countries could provide F-16s?
At the moment, there are around 25 countries that currently operate the F-16.
The fighter jets come at a high price, and Bell says that although many countries have them, “none of them have spare aircraft.”
He adds: “They’re just too expensive. You generally buy what you can afford and that’s not enough for everything you want to have them for.
“So none of the nations will be able to get rid of excess jets. But I suspect what will happen is that they will need to focus on a commonality of jets.
“So who operates a certain block and a certain age of aircraft and see whether there is some shuffling behind the scenes that different countries can give each other aircraft so that you get a common aircraft that comes to Ukraine.”
How soon could Ukraine start using them?
US officials have estimated that it could take 18 months for training and delivery of the jets.
On Monday, Emmanuel Macron said France was open to training Ukrainian pilots straight away.
London has agreed to start training pilots in the spring and said it would look at shortening the sessions for experienced Ukrainian pilots.
UK Defence Secretary Ben Wallace said on Wednesday: “This is not about gifting weapon systems.
“This is about gifting a platform. If anyone follows Formula One, you don’t just gift a car, you have to gift a pit team.”