 Spark-gap transmitter

The first type of device that allowed sending Morse code without wires, as opposed to the wired electrical telegraph that previously existed.

Naval communications was one of the first major applications, as you can't have wires on boats!

Wireless voice transmission came about with modulation.

A spark-gap transmitter is an early type of radio transmitter that uses a spark gap to create radio frequency (RF) signals. It was one of the first practical methods of generating radio waves for wireless communication, primarily used in the late 19th and early 20th centuries.