Analysis: The logistical and cost problems behind any European presence in Ukraine
By Sean Bell, Sky News military analyst
Sir Kier Starmer has stated the UK is "ready and willing" to put troops on the ground to help guarantee its safety in a future peace deal.
The US has made clear it has no intention to put US "boots on the ground", and although many European nations are looking at ways to support Ukraine, some - like Poland - have made clear they currently have no plans to commit land forces to Ukraine.
For clarity, the UK's prime minister is not committing UK forces to the current conflict; however, it is not entirely clear in what capacity any committed forces might be involved, should they be deployed.
Traditional peacekeeping roles are conducted by UN forces that are seen as impartial, but if the UK and European partners are involved, they would clearly be viewed by Russia as being biased, placing the forces involved at risk.
The challenge is how to provide enduring security guarantees to Ukraine now the US has made clear Ukrainian membership of NATO is not an option.
President Trump sees China as the US priority, and as the Russian invasion of Ukraine is on the European continent, he sees the long-term security implications of Russian aggression as a European responsibility.
If some form of enduring international military presence is required to maintain any post-conflict peace between Russia and Ukraine, that would involve a significant land footprint.
The numbers problem
As a minimum, most analysts believe at least 100,000 soldiers would be required to create a credible military stabilisation force, albeit some estimates - particularly those from President Zelenskyy - suggest this could be a very conservative number.
The largest military powers in Europe might be expected to take the lead for any such military task - UK, France and Germany - but the scale of the requirement poses significant issues for a continent that has seen its collective military capability atrophy over the past few decades.
By way of example, the British Army's current strength is around 74,000, so at face value the challenge of mounting a 100,000, multi-national force looks achievable.
However, not all army personnel are available for war-fighting duties - many are involved in training, logistics, procurement and other vital supporting roles.
Optimistically, we might expect up to 50% of the total strength to be available for deployment, although this would probably leave no contingency capability.
Rotation issues
If we also assume any such deployment would be enduring, the British army contingent would need to be rotated periodically.
If forces were deployed for six months at a time, they would need a similar number undergoing training ready for deployment, and a third element recovering from deployment and taking leave.
Assuming 30,000 troops were available for deployment, the British army would therefore be able to sustain a deployed force of 10,000 personnel.
This represents only 10% of the forces required.
If Germany and France were able to provide a similar scale of commitment, that would still only represent 30% of the total forces required.
Without US military support, an enduring and credible European military commitment would be very difficult to deploy and sustain.
Cash is not a quick fix
Historically, Europe might have expected the US to shoulder the majority of any military burden in such circumstances, but President Trump appears to be using the Russian invasion as an incentive for Europe to take responsibility for collective defence, and not rely on US military capability (and investment) for their domestic security.
However, even if Europe were to double their investment in collective military capability overnight to 5% of GDP, as suggested by Trump, it would be years before the European Defence Industrial Base would have the capacity to turn cash into military equipment.
Although European leaders have a raft of competing demands for national resources, the priority for any nation is national defence.
National defence is an insurance policy against an uncertain future - failure to pay for a robust military capability leaves nations vulnerable.
Many NATO nations have enjoyed a significant peace dividend following the end of the Cold War.
However, decades of under-investment in defence have now left critical vulnerabilities, both nationally and in the alliance.
What needs to be done is clear - the issue is how, and at what cost.
