On its face, the Pentagon’s reported decision to send thousands of 155mm artillery, originally destined for Ukraine, to Israel seems to validate the argument critics of US assistance to the besieged Eastern European nation make: Aid to Ukraine is a distraction from America’s true priorities, both in the Middle East and in the Indo-Pacific.

Nothing can be further from the truth.

In the immediate short run, policymakers might have to make delicate judgment calls.

What matters more, however, is US assistance to Ukraine has already helped reveal shortcomings in our defense-industrial base.

And it has already provided an initial impetus, however modest, to fix some of the flaws.

Roughly 60% of US aid to Ukraine, or $68 billion, is spent in the United States on contracts that help replenish the Pentagon’s reserves with new equipment.

And the new contracts enable suppliers to scale up their production and open new lines — not to speak of job creation — which will come in handy if America is faced with Chinese aggression over Taiwan.

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The fact America’s defense industry, along with European allies’, is in terrible shape is not Ukraine’s fault.

Responsibility lies with leaders on both sides of the Atlantic who took full advantage of the “peace dividend” after 1990, assuming large-scale armed conflicts were a thing of the past.

In reality, the best way to deter such conflicts is for the United States and its allies to maintain a large defense industry, capable of springing into action quickly.

The World War II experience is instructive.

At the war’s start, the US defense industry was already the largest in the world; yet in the four subsequent years it doubled in size, producing two-thirds of all allied military equipment.

“During an 11-month span in 1942,” my AEI colleague Mackenzie Eaglen notes, “over 8,000 of the United States’ standard tank during World War II, the M4A3 Sherman, were built — a monthly average of 729.”

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The reason for this success was the growth in demand for US military equipment both before and during the war, which was facilitated by the Lend-Lease program.

If it hadn’t been for those early orders before America entered the war, the United States would have been in a much worse starting position once it entered the conflict.

Today, the Army-owned plant in Lima, Ohio, builds between 15 and 20 Abrams tanks a month (down from almost 70 a month during the Cold War), which it could boost to 33.

Expanding production further would mean hiring another shift of workers — something that makes sense only if there is a sustained flow of money from US and overseas contracts.

The production of 155mm shells suffers from a similar predicament — or at least did until recently.

Every day, Ukrainians fire between 6,000 and 8,000 rounds, burning through available reserves quickly, particularly those of NATO countries.

At the same time, governments are pushing manufacturing to scale up their production capabilities.

The United States produces around 28,000 shells each month, double the monthly output from half a year ago.

By 2025, the Pentagon aims to bring the monthly total to 100,000.

Even French manufacturers are on track to triple production in the course of this year, albeit starting from very modest levels (1,000 shells a month).

Barring the possibility of a large regional conflagration instead of a targeted intervention in Gaza, Israel’s needs for 155mm shells are not going to be anywhere near those of Ukrainians’.

But the more important point is that Ukrainian demand for shells (or other equipment) and our willingness to provide them while replenishing our own reserves makes it easier to produce even more, should the need arise.

For policymakers in Taiwan, the waiting times for US-made equipment ordered years ago is a source of frustration.

Yet Taiwanese policymakers understand US aid to Ukraine is not only an important deterrent measure keeping Beijing at bay — it helps accelerate production, which would have otherwise been much slower at lower volumes of output.

Whatever his many flaws, President Biden was entirely correct to say in his speech Thursday that helping Ukraine, Taiwan and Israel was “a smart investment that’s going pay dividends for American security for generations.”

What he didn’t say is there is a common thread going through Russian, Chinese and Iranian revisionism — and that how strongly we respond to each of those directly affects our chances in the remaining two conflicts.

Our defense-industrial base is a big reason why.

Dalibor Rohac is a senior fellow at the American Enterprise Institute. Twitter: @DaliborRohac.