The US has approved delivery of F-16 warplanes from the Netherlands and Denmark to Ukraine, officials in Washington and Europe said, although the aircraft are unlikely to go into operation any time soon. It was not clear when the first F-16s might enter the conflict, as Ukrainian pilots will require at least six months of training on the aircraft. US National Security Adviser Jake Sullivan said Secretary of State Antony Blinken sent a letter to his Dutch and Danish counterparts this week, offering formal assurance that the US would fast-track approval of all requests from third parties to transfer F-16s to Ukraine. Ukraine has asked for a fighter that might give it a combat edge. Last month, it began a long-anticipated counteroffensive against the Kremlin’s forces without air cover, placing its troops at the mercy of Russian air attack and artillery. US Air Force Gen James Hecker, commander of US air forces in Europe and Africa, told reporters in Washington on Friday that he did not expect the F-16s to be a game-changer for Ukraine. Preparing squadrons for battle could take “four or five years”, he said. In eastern Ukraine, attack helicopter pilots told Associated Press that they welcomed the news. They said Russia had air superiority, but the introduction of US jets could shift the balance of power. Capt Yevgen Rakita, a spokesman for the 18th Army Aviation Brigade, said the Ukrainian Air Force was supporting infantry with decades-old Soviet-era planes which are vulnerable to Russian air-to-air and ground-to-air missiles. “A modern war cannot be won without aviation” capabilities, he said. In making the decision on F-16 deliveries, Washington aims to ensure warplanes can be provided to Ukraine as soon as its pilots complete training, according to a US administration official. Dutch Foreign Minister Wopke Hoekstra welcomed the US decision. The move is a “major milestone for Ukraine to defend its people and its country”, he said in a post on X, formerly Twitter. Danish Defence Minister Jakob Ellemann-Jensen said the training of Ukrainian pilots would start this month. A coalition of 11 western countries – the Netherlands, Belgium, Canada, Denmark, Luxembourg, Norway, Poland, Portugal, Romania, Sweden and the United Kingdom – pledged in July to train Ukrainian pilots to fly F-16s. Denmark will hand over some of its F-16s only after receiving its F-35 Lightning fighters. The first four F-35s are scheduled to be delivered on October 1. Washington's approval for the plane donations is needed because the aircraft are built in the US. Ukraine's western allies have at times moved slowly on granting Kyiv the military support it has requested. President Joe Biden's authorisation in May for allies to train Ukrainian forces on how to operate the F-16s, and eventually to provide the aircraft themselves, was preceded by months of debate in Washington and talks with allies, officials said. The administration said it had concerns that the move might escalate tensions with Russia. Also, US said argued that learning to fly and logistically support the F-16 would be difficult for Ukrainian forces trained on post-USSR era planes. Delivery is likely to be months away, but Washington claims the F-16s – like the Abrams tanks it has promised – will be crucial for Ukraine's long-term security. Ukraine has been relying on older aircraft, such as Russian-made MiG-29 and Sukhoi jets. F-16s have newer technology and targeting capabilities. They are also more versatile, analysts said.