To America’s anxious allies, President Donald Trump ’s plans for a big boost to the US defence budget might appear to be welcome news. It seems to offer reassurance that despite the strong strand of “America first” isolationism in his campaign, the new president is committed to upholding America’s strategic commitments, and preserving its role as the guarantor of peace and stability in key regions like Europe and East Asia. But it would be a mistake to see the president’s defence budget announcement this way. There is much less to it than meets the eye, and little that offers any serious hope that America under Donald Trump will respond effectively to the strategic challenges that it has inherited from Barack Obama. Let’s start with the numbers. As always with defence budgets, there is a much scope for confusion, but however you cut it, Trump’s boast of a historic 10 per cent rise in defence spending looks overblown. The White House itself has reportedly acknowledged that the spending proposed for the next fiscal year is only 3 per cent above this year’s projection, and inflation will eat up most of that. The amount of extra money actually flowing into building and maintaining combat capabilities is thus going to be very limited at best. What difference any extra money makes to America’s ability to meet its challenges depends of course on how it is spent. So far, there are few details, but Trump’s focus is plainly on big-ticket, high-profile major equipment. His centrepiece is a plan to expand the US Navy to 350 ships , from the current 274. There are several problems with this approach. For one thing, this may not address the most urgent constraints on US military power. Like many modern militaries, US forces struggle to find the funds to maintain and operate the capabilities they already have. Filling these funding gaps is often the most effective way to enhance combat power, while spending the money buying more expensive ships and aircraft, which then also need to be maintained, only exacerbates the problem. Moreover, investing in major new equipment takes a long time, and requires sustained funding over decades. No matter how much money he commits, Trump’s initiatives will not deliver any extra ships for a decade at least. And how can he be sure that America’s rivals like China will not simply match his spending with defence budget increases of their own? Vague talk of upholding a rules-based global order might sound good in a lecture hall, but it would carry little weight in the White House Situation Room at 3am But above all, the idea that spending more money on things like building more ships will help restore US strategic pre-eminence reflects deep misunderstanding of the nature of the challenges that American leadership faces in Asia and elsewhere. There are two aspects to this. First, on the purely military level, America’s problems cannot be solved by a few dozen more ships, aircraft or infantry battalions. In Eastern Europe, for example, the balance of conventional military power lies so heavily in Russia’s favour that even doubling the size of the US Army would do little to improve the chances of a quick, cheap and decisive American victory in a conflict over Ukraine or the Baltic States. Likewise, more ships in the navy will do little to meet China’s challenge to US military preponderance in Asia. Indeed they will, in a sense, only make the problem worse. That is because the key to the shifting maritime military balance in the Western Pacific in Asia is the growingvulnerability of surface warships to torpedoes and missiles launched from submarines, aircraft and land bases. For over 20 years now, China has been working to exploit this growing vulnerability by building forces that can find and sink US naval ships. That allows it to raise the costs and risks to America of projecting power by sea into the waters of the East Asian littoral around China. And that in turn undermines US regional strategic leadership, which has always depended on America’s ability to project massive military power into those waters aboard its aircraft carriers and marine amphibious ships. Building more ships won’t solve that problem, because more ships just means more targets for Chinese missiles. That is especially true of the new aircraft carriers that Trump promised to build as the centrepiece of his plans to revive America’s military power, when he went aboard America’s newest carrier, the USS Gerald R. Ford, this month. But there is real doubt that these immensely expensive, increasingly vulnerable behemoths would ever be risked in a major naval combat zone again, and whether, if they were, they would do the enemy enough harm to justify their cost. Can China leapfrog the US in the scramble for the world’s best aircraft carrier? Will Donald Trump aggravate the China-US arms race? Indeed, America will only be able to sustain its place as a major power in Asia if it completely overhauls its military strategy there to take account of the huge changes in naval warfare since the carriers’ heyday 70 years ago. Projecting air power and marine forces in vulnerable ships will not work against the new anti-ship capabilities leveraging modern surveillance and guidance technologies. America will need to go with the technological flow by focusing on preventing its adversaries projecting power by sea, rather than swimming against it by trying to project power by sea itself. Does America still have the resolve to fight a major war in Asia or Europe against powers as strong as China and Russia? But that still leaves the biggest question of all unanswered. Does America still have the resolve to fight a major war in Asia or Europe against powers as strong as China and Russia? Back in the cold war, this was never seriously in doubt, but today it is much less clear. US allies in Europe and Asia must ask themselves why, in today’s world, Washington would risk a major war against a nuclear adversary to defend their interests. Vague talk of upholding a rules-based global order might sound good in a lecture hall, but it would carry little weight in the White House Situation Room at 3am, facing even a remote risk of a nuclear attack on a US city. Especially when the person at the head of the table is Donald Trump. Ultimately, spending more money on defence makes little difference to the final strategic outcome unless you are willing to use your forces to go to war – and unless you can convince both your allies and your adversaries of that. And that is something Trump will find very hard to do, no matter how big his defence budget grows. Hugh White is professor of strategic studies at the Australian National University in Canberra