Modern warfare is awash with cutting-edge technology—from AI to drones to hypersonic missiles—yet one technology that is more than a century old is still proving its worth: Morse code.

Inventor Samuel F. B. Morse spent summers at his Locust Grove Estate in New York's Hudson Valley. The 14,000-square-foot Italianate villa, built in 1852, has 45 rooms over six floors. It was ...