He was active in the Spanish navy during the reign of the Holy Roman Emperor, Charles V. He made several important inventions, including a diving apparatus, and introduced the paddle wheel as a substitute for oars.

[1] In the nineteenth century, a Spanish archivist claimed to have discovered documents that showed that de Garay had tested a steam-powered ship in 1543.

At the time there were several people of the Garay name who distinguished themselves in letters and in the military service who seem to have been from the minor nobility in the Castilian city of Toledo.

The most plausible account is that he was an impoverished minor nobleman, educated in letters, who out of necessity went into the King's service but, as he wrote, dedicated himself to the sciences and invention.

González stated that in a file he had found, there is documentation endorsing a test conducted June 17, 1543[5] by the Naval Captain and Engineer of the navy of Charles V of a navigation system with no sails or oars containing a large copper of boiling water.