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The new proposed American defense budget for 2015 complies with the law ^[2] that requires additional cuts in American military spending. A temporary deal reached in December would soften the planned sequestration cuts for this year and next, but the budget would continue to decline, descending to about $500 billion by mid-decade (including Department of Energy nuclear weapons costs as well as those for the Department of Defense, and modest assumed war costs at that point as well).

By one measure, this is still an enormous amount of money (and still nearly 3% of US GDP), even if it would reflect a reduction of $200 billion relative to the peak war years of a few years ago. And it still modestly exceeds the US Cold War average as well as the pre-9/11 norm ^[3]. It would still represent more than twice China’s expected military spending at that point as well.

However, the real metric of adequacy shouldn’t be raw dollars, of course, but capability. I’ll focus here on two central questions. One: under the new plan, will the US ground forces (and particularly the Army, which bears the brunt of the cuts) still be large enough for demands in Asia and beyond? Two: will the Navy be able to sustain its central role in the so-called Asia-Pacific rebalance?

How much army is enough?
The Pentagon’s new strategy calls for an active-duty Army of just 450,000 soldiers—the fewest fulltime soldiers the country would field since before World War II, though only 10% less than the average of the late Clinton and early George W. Bush years. Is that enough?

Since 1992, this country has based its planning for ground forces around the possibility of fighting two large regional wars at once. Now Saddam is gone, Iraq is violent but not looking to invade anybody, and all the military buzz is about drones, cyber, space, SEALs, and long-range strike systems. And since 2012 the Pentagon has declared the end of any interest in large-scale counterinsurgency and stabilisation missions. Most Americans, chastened and fatigued by the Iraq and Afghanistan experiences, might happily go along with this new way of thinking.

But this logic could go too far. If sequestration kicks back in by 2016, as current law would now have it do, Pentagon plans may cut the active Army to 400,000 or below. A former Chief of Naval Operations recently proposed cutting it below 300,000 ^[4] (PDF). These are not wise ideas.

The Army, together with the Marine Corps and other elements of our military, still needs to continue to deter conflict against North Korea—a nation now armed with perhaps 10 nuclear bombs, and a million active-duty indoctrinated soldiers with perfectly serviceable AK-47s and other small arms. If, heaven forbid, there’s another war on the Korean peninsula, our South Korean allies will need lots of American help to prevent the destruction of Seoul and the possible seepage of nuclear materials onto the international black market where terrorists could bid for them.

Then there are all the other, smaller, possible missions. To be sure, we shouldn’t let our imaginations run completely rampant. I’m glad nobody was talking about sending US troops to Ukraine during the recent crisis there. We also needn’t plan to fight China on the Asian mainland, or go chase drug kingpins with US Army forces in Mexican mountains, or occupy Iran or Pakistan to seize their nuclear capabilities. Some missions are just too hard, too dangerous, too peripheral to US interests—or simply undoable.

But other possible missions could arise. Nobody saw the Bosnia and Kosovo missions coming until the Balkans exploded in violence in the 1990s. Korea wasn’t on our radar screen in 1950; Vietnam barely registered in the early 1960s; Afghanistan was about the least likely place anybody thought we’d send troops until 2001.

Here are some missions we can’t rule out:

• An international implementation force to uphold any deal the belligerents in Syria might ultimately accept
• American battalions or brigades of up to a few thousand troops per country to shore up our Persian Gulf allies after a possible American military strike to eliminate Iran’s nuclear facilities (if talks fail), followed by a prolonged period of low-intensity conflict with Iran thereafter
• A peacekeeping mission to secure and stabilise Kashmir after disputes over that province possibly lead India and Pakistan to their fifth war—and the prospect of their first nuclear war
• An implementation force for an Israeli–Palestinian peace deal

None of these scenarios is likely to happen, but as noted, we tend to wind up in one or two such missions at a time over any given decade. So planning for one big war—like Korea—to shore up deterrence, while having the capacity to help backstop two multinational stabilisation missions elsewhere, is a reasonable way to plan future US ground forces. We can probably, by my calculations, satisfy that requirement with 450,000 active-duty soldiers. But not much less.

The Navy and the rebalance
Under policies announced at the annual Shangri-La conferences in recent years, the US Navy will now base 60% rather than 50% of its fleet on the Pacific side of the world. In fact, ships based in that region can still reach the Persian Gulf easily enough, so this represents an upper bound on the additional assets devoted to the Asia-Pacific per se.

One useful, minimal measure of whether the rebalance is still alive and well is whether 60% of our future Navy will clearly exceed the capacity of 50% of our previous Navy. If not, it’s hard to take the rebalance seriously, despite a few thousand additional Marines in Australia at times, and a few small ships operating out of Singapore.

By this measure, we’re probably OK for now—but only if sequestration doesn’t return. The old, pre-rebalance Navy was about 300 ships, so half of that fleet was 150 vessels. The current Navy is about 285 strong, headed for perhaps 280 if Hagel and Obama have their way, but to perhaps 270 in the short term and as few as 250 thereafter if sequestration-scale cuts return. And 60% of a 250 ship Navy is no larger than 50% of the former fleet.

So sequestration would, to my mind, effectively kill the rebalance. At present, it’s a limited effort but it’s still intact, as a reaffirmation and reinvigoration of American commitment to the Asia-Pacific region—but just barely. US defense cuts have gone far enough, and if anything, it’s time to think about beginning to reverse them, at least modestly.

Michael O’Hanlon is senior fellow at Brookings. Image courtesy of Flickr user U.S. Air Force ^[5].