The shell crisis of World War I reminds us just how hard it is to prepare for long wars. “In almost every war there comes a point when it's clear that the peacetime defense industry, even if it had been ramping up, is inadequate for the demands of war,” says Mark Cancian, a retired Marine Colonel who is now a senior adviser at the Center for Strategic and International Studies (CSIS).  

More than a century later, the world, and warfare, have changed. But even in a world of fighter jets, nuclear weapons, satellite communications, drones, and AI, ammunition still matters. The decline of the British Empire was followed by the rise of the United States as Earth’s military superpower, the Cold War's onset and end, and numerous conflicts throughout the Middle East. Now, America faces an arms shortage of its own. Even given the historical precedent, the current U.S. predicament is stunning. 

The United States spends more on defense than the next seven countries combined, including rivals China and Russia. And yet, the U.S. military finds itself concerned about running short of key munitions in a war with a country, Iran, that could generously be described as a “middle” power.