The United States, the Netherlands and Denmark announced Wednesday that the transfer of the planes had begun, saying Ukraine "will be flying operational F-16s this summer."

Zelensky had repeatedly pushed for the US-made warplanes to help counter Russia's invasion, with the United States eventually acceding last year after initially insisting that focusing on ground-based air defenses was a better use of resources.

"As a symbolic effort, it's tremendously important... This was really the last item that Zelensky had highlighted as important for Ukrainian defense," said Mark Cancian, a senior advisor at the Center for Strategic and International Studies.

He noted that there has been a series of weapons systems -- HIMARS rocket launchers, Patriot air defense batteries, Abrams tanks, ATACMS missiles -- that Washington was reluctant to provide but eventually agreed to donate to Kyiv.

"In each case, providing that weapon had an important symbolic and psychological impact, putting aside, you know, what the battlefield impact might be," Cancian said.

"I think it will help for air defenses... but it's not going to be a silver bullet," he said of the F-16s, noting that there "just aren't going to be enough of them."

- Devastating strikes -

Zelensky said in an interview with AFP in May that Kyiv needed up to 130 F-16s to secure air parity with Russia, but Western countries have pledged fewer than 100 so far, and not all of them will arrive at once.

Russia has exploited gaps in Ukraine's air defenses to carry out devastating strikes on civilians and infrastructure, as well as to pummel Kyiv's troops on the front lines, leaving the country desperate for additional protection.

Highlighting the threat, more than 40 people were killed earlier this week by a wave of dozens of missiles that hit cities across the country and ripped through a children's hospital in Kyiv.

The lack of air superiority has also hampered Ukrainian operations, with Kyiv pointing to that as a major factor limiting its forces' ability to advance following a lackluster 2023 counter-offensive.

Zelensky hailed the announcement that F-16s were being transferred, saying the planes will "bring just and lasting peace closer, demonstrating that terror must fail everywhere and at any time."

- Air defense symphony -

Cancian said air defense will likely be Ukraine's main use for the planes, along with supporting frontline troops and a few "high-visibility deep strikes" inside Russia.

Michael Bohnert, an air and maritime acquisitions expert with the RAND Corporation, said the transfer of the F-16s "shows a long-term commitment" to Ukraine.

"The logistics and support for these aircraft, including training etc., is a long-term process, and it is a tangible, measurable way of showing a long-term commitment," he said.

Bohnert said the F-16s will be able to help "chase down cruise missiles like those used in the attacks on Kyiv," and also to defend areas where there are no ground-based systems.

The planes could also divert Russian resources toward countering them in the air and seeking to destroy them on the ground, he said.

Bohnert said "it's not just one system, it's a symphony. And right now, Ukraine, their air symphony's a little thin, and they don't have every instrument."

"This is like adding brass instruments when you already have... percussion, strings, etc. It's just adding another piece," he added.