Soldiers in Germany’s Light Infantry Battalion 413 near the Baltic Sea coast complained last year that they didn’t have enough sniper rifles or antitank weapons or the right kind of vehicles.

During exercises, they told a parliamentary ombudsman, their unit didn’t have the munitions to simulate battle. Instead, they were told to imagine the bangs.

Across Europe, similar shortfalls riddle land, sea, air and cyber forces following years of defense cutbacks.

U.S. President Donald Trump last month irked European leaders when he berated them at the North Atlantic Treaty Organization’s new headquarters for insufficient defense spending and what he called unpaid military bills.

Current and former European officials were quick to point out that NATO members don’t owe dues to the U.S., but they acknowledged Mr. Trump wasn’t wrong: Europe lacks the capabilities to defend itself.