The Netherlands and Denmark have led a push to train Ukrainian pilots to fly F-16s and deliver the fighter jets to Ukraine to help counter Russia's air superiority.
Here are some facts about the alliance of Western countries that will supply aircraft and training:
HOW MANY F16S WILL UKRAINE GET?
Denmark will deliver 19 jets in total with the initial six due around the end of the year, followed by eight in 2024 and five in 2025, Danish Prime Minister Mette Frederiksen said on Aug 20.
The Netherlands has 42 F-16s available but has yet to decide whether all of them will be donated.
WHEN WILL TRAINING START?
Denmark this month began training eight Ukrainian pilots in flying the jets, the Danish armed forces said.
The eight pilots arrived at the Danish military air base in Skrydstrup along with 65 personnel who will be trained in maintaining and servicing the jets.
Greece will also take part in the training, Ukrainian President Volodymyr Zelenskiy said.
Officials from a coalition of 11 nations have said F-16 training will also take place in Romania.
WHAT WILL F-16S DO FOR UKRAINE'S WAR EFFORT?
Zelenskiy called the donation a "breakthrough agreement" and said the planes would strengthen Ukraine's air defences and help its counter-offensive against Russian forces.
U.S. officials have privately said F-16s would have been of little help to Ukraine in its current push and will not be a game changer when they eventually arrive given Russian air defense systems and contested skies over Ukraine.
Poland and Slovakia have supplied 27 MiG-29s to supplement Ukraine's fleet of combat aircraft.
HOW SOON COULD UKRAINE START USING THE F-16?
A Ukranian air force spokesman has said he did not expect Ukraine to be able to operate F-16 jets this coming winter.
Ukraine's Defence Minister Oleksiy Reznikov has said six months of training was considered the minimum for pilots, but it was not yet known how long it would take to train engineers and mechanics.
The training programme should leave Ukrainian pilots and service personnel able to use F-16s in combat by early next year, NATO leaders said in July.
WHAT ARE THE CHALLENGES?
Designed in the 1970s and produced in the 1980s by General Dynamics, now a part of Lockheed Martin, the F-16 jets that Ukraine will receive are around 40-years-old.
While the weapons systems and instruments have been updated, the air frames are subject to heavy maintenance needs, said Esben Salling Larsen, a military analyst at the Royal Defence College.
"The Ukrainians will have to use a lot of their time on maintenance of the jets," Salling Larsen said.
Another challenge is the time pressure on the training of the pilots, engineers and mechanics.
The F-16s are U.S.-made whereas Ukraine's current jets are Russian, creating the challenge of a language barrier for mechanics and engineers.
WHAT ARE THE BENEFITS?
F-16s have been on Ukraine's wish list for a long time because of their destructive power and global availability. The aircraft is equipped with a 20mm cannon and can carry bombs, rockets and missiles.
Many NATO allies have F-16s, making it easier to find spare parts compared with the Russian planes currently used by Ukraine.
Denmark and other countries have also started to use other jets such as the F-35s on order by Denmark, boosting the supply of spare parts from retired planes.
WHAT IS RUSSIA SAYING?
Russia warned that supplying jets to Ukraine would escalate the war.
"The fact that Denmark has now decided to donate 19 F-16 aircraft to Ukraine leads to an escalation of the conflict," Russian ambassador Vladimir Barbin said.
WHO ELSE MIGHT DONATE JETS?
Norway is considering whether to donate F-16s but has not said how many.
Portugal, Romania and Belgium all have F-16s like those donated by Denmark and the Netherlands making them suitable for a donation as Ukrainians are being trained for these jets.
Ukraine last week began discussing with Sweden the possibility of receiving Swedish-made Gripen jets.
In June, Sweden said it would give Ukrainian pilots the opportunity to test its Saab-made Gripen fighter, but it has also said it needs all its planes to defend Swedish territory.
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