What are the Storm Shadow missiles Ukraine has fired into Russia?

Storm Shadow is an Anglo-French cruise missile with a maximum range of around 250km (155 miles). The French call it Scalp.

It is launched from an aircraft, then flies at close to the speed of sound, hugging the terrain, before dropping down and detonating its high explosive warhead.

Storm Shadow - made by manufacturer MBDA - is considered an ideal weapon for penetrating hardened bunkers and ammunition stores, such as those used by Russia in its war against Ukraine.

But each missile costs nearly US$1m (£767,000), so they tend only to be launched as part of a carefully planned flurry of much cheaper drones, sent ahead to confuse and exhaust the enemy’s air defences, just as Russia does to Ukraine.

They have been used with great effect, hitting Russia’s Black Sea naval headquarters at Sevastopol and making the whole of Crimea unsafe for the Russian navy.

Justin Crump, a military analyst, former British Army officer and CEO of the Sibylline consultancy, says Storm Shadow has been a highly effective weapon for Ukraine, striking precisely against well protected targets in occupied territory.

"It’s no surprise that Kyiv has lobbied for its use inside Russia, particularly to target airfields being used to mount the glide bomb attacks that have recently hindered Ukrainian front-line efforts," he says.

The UK had supplied Storm Shadow missiles to Ukraine for months but, like the US, had not allowed Kyiv to use them to strike inside Russia.

But this changed after the Biden administration updated its rules, allowing comparable Atacms missiles to be used outside of Ukraine's borders.

On Wednesday, it was confirmed Ukraine used UK-supplied Storm Shadow missiles against targets inside Russia for the first time.

The Ministry of Defence has not yet publicly commented. But the UK government was known to have been supportive of allowing Ukraine more freedom to use missiles as it saw fit, although it had followed US policy.

Its most immediate priority is blunting the expected Russian counter-attack on Ukrainian positions in the Kursk region of western Russia.

But Ukrainian cities and front lines are also under daily bombardment from Russia.

Many of the missiles and glide bombs that wreak devastation on military positions, blocks of flats and hospitals are launched by Russian aircraft far within Russia itself.

Kyiv has said that not being allowed to hit the bases these attacks were launched from was akin to making it fight this war with one arm tied behind its back.

Ukraine does have its own, innovative and effective long-range drone programme.

At times, these drone strikes have caught the Russians off guard and reached hundreds of kilometres inside Russia.

But they can only carry a small payload and most get detected and intercepted.

Kyiv argued that in order to push back the Russian air strikes, it needed longer-range missiles, including Storm Shadow.

The US decision to allow the use of its own long-range missiles is also intended to help Ukraine defend the small chunk of Russian territory it currently occupies in the Kursk region. A major assault by Russian and Northern Korean troops is expected.

With the green light to use long-range missiles, airfields and key logistics hubs deep inside Russia have also come within Ukraine’s range.

Kyiv has been asking to use long-range Western missiles inside Russia for so long that Moscow has already taken precautions.

It has moved bombers, missiles and some of the infrastructure that maintains them further back, away from the border with Ukraine and beyond the range of Storm Shadow.

There is scepticism among Western officials that Storm Shadow and the American Atacms will be decisive.

However, the Institute for the Study of War think tank (ISW) has identified around 225 Russian bases that would be in range of Storm Shadows fired from Ukraine.

And Sibylline's Justin Crump says that while Russian air defences have evolved to counter the threat of Storm Shadow within Ukraine, this task will be much harder given the scope of Moscow’s territory that could now be exposed to attack.

"This will make military logistics, command and control, and air support harder to deliver, and even if Russian aircraft pull back further from Ukraine’s frontiers to avoid the missile threat they will still suffer an increase in the time and costs per sortie to the front line."

Matthew Savill, director of military science at the Rusi think tank, believes it could also pose a dilemma for Russia as to where to position air defences, which could make it easier for Ukraine’s drones to get through.

Ultimately though, says Savill, Storm Shadow is unlikely to turn the tide. Ukraine doesn't have many missiles, and the UK has very few left to give.