What are ATACMS and could the longer-range weapons change the war for Ukraine?

The U.S. will allow Ukraine to use American-supplied longer-range weapons to conduct strikes inside Russian territory, a long-sought request by Kyiv, according to published reports from the New York Times and Reuters.

It was not clear if there would be limits on Ukraine's use of the Army Tactical Missile System, or ATACMS, as there have been on other U.S. missile systems. Their deployment could at least initially be limited to Russia's Kursk region, where Ukrainian troops seized territory earlier this year.

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Duration 4:43

Months after sending long-range missiles to Ukraine, the White House has given the green light to use their full force against Russia. This comes after the worst aerial attack against Kyiv in months and questions about how Donald Trump will change the course of the war.

Since the first year of the war, Ukrainian leaders have lobbied Western allies to allow them to use advanced weapons to strike key targets inside Russia a move they hope would erode Moscow's capabilities before their troops reach the eastern front line. It could also serve as a deterrent in the event of future ceasefire negotiations.

Washington long opposed the move, with President Joe Biden determined to avoid any escalation that he felt could draw the U.S. and other NATO members into direct conflict with nuclear-armed Russia. The Kremlin warned Monday that the decision adds "fuel to the fire."

The decision comes in the waning days of Biden's presidency, before president-elect Donald Trump, who has said he would bring about a swift end to the war that many fear could force unpalatable concessions from Kyiv, assumes office.

The policy change came "too late to have a major strategic effect," said Patrick Bury, a senior associate professor in security at the University of Bath in the United Kingdom.

"The ultimate kind of impact it will have is to probably slow down the tempo of the Russian offensives which are now happening," he said.

What are ATACMS?

Pronounced like "attack 'ems," the ballistic missiles developed by U.S. aerospace and defence company Lockheed Martinhave nearly double the striking distance up to 300 kilometres of most of the weapons in Ukraine's possession. They can carry out pinpoint attacks on airfields, ammunition stores and strategic infrastructure.

The United States supplied Ukraine with ATACMS last year and they have been used to destroy military targets in Russian-occupied territories of Ukraine but not on Russian soil.

Why does Ukraine say it needs longer-range weapons?

Ukraine has been asking its Western allies for longer-range weapons in order to alter the balance of power in the war where Russia is better resourced, and strike with precision airbases, supply depots and communication centres hundreds of kilometres over the border.

It hopes the weapons would help blunt Russia's air power and weaken the supply lines it needs to launch daily strikes against Ukraine and to sustain its military ground offensive into Ukraine.

If used in Kursk, the weapons would likely require Russian forces preparing for counterattacks to push back valuable equipment and manpower and complicate battle plans.

In lieu of Western weapons, Ukraine has been regularly striking Russia with domestically produced weapons, with some capable of travelling up to 1,000 kilometres, but it still lacks sufficient quantities to do serious long-term harm.

Washington has permitted Ukraine to use its weapons systems inside Russian territory on one known occasion previously. In May, after Russia's offensive into the Kharkiv region threatened to stretch Ukrainian forces thin, Biden permitted the use of High-Mobility Artillery Rocket Systems (HIMARS) with a range of 80 kilometres to quell that advance.

Will the decision change the course of the war?

If strikes are allowed across all of Russia, they could significantly complicate Moscow's ability to respond to battlefield demands.

If strikes are limited to the Kursk region, Russia could relocate its command centres and air units to nearby regions, blunting the effect of those logistical challenges. That would also mean many of the valuable targets Ukrainian officials have expressed desire to hit may still be beyond reach.

Pentagon spokesperson Lt.-Col. Charlie Dietz has noted the ATACMS wouldn't be the answer to the main threat Ukraine faces from Russian-fired glide bombs, which are being fired from more than 300 kilometres away, beyond the reach of ATACMS.

Ukrainian leaders have also said that Russian forces have had time to pull back assets beyond the range of the missiles in the time it has taken the U.S. to make the decision.

"The decision came far too late. Had it been made at the beginning of the fall, it might have disrupted Russia's counteroffensive in the Kursk region. And if it had been made even earlier, it could have derailed the offensive in the Pokrovsk direction," said Glib Voloskyi, an analyst at the CBA Initiatives Center, a think-tank.

In addition, the overall supply of ATACMS is short, so U.S. officials in the past have questioned whether they could give Ukraine enough to make a difference.

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However, the decision may also encourage Britain and France to allow Ukraine to use Storm Shadow missiles, also known as SCALP missiles, with a range of 250 kilometres.

British Defence Minister John Healeyon Monday said the U.K. government would "give Ukraine the support that it needs and do so for as long as it takes," but that he wouldn't "compromise operational security and comment on the details of long-range systems today."