Kevin L
A True Doomsday Prepper
Not to take away from all the great things Jules Verne predicted...but...
20,000 Leagues Under the Sea was published in 1870.
The H L Hunley (CSA) was the first submarine to sink an enemy ship...in 1864.
I also guess this depends upon your definition of a submarine.
The ancient Macedonian Alexander the Great was said to have personally explored the undersea world in a glass diving bell. He took notes, took specimens, and made drawings of his findings, but these were lost when the great library in Alexandria (now Cairo) was torched and sacked.
He was able to propel his diving bell by walking (the Confederate sub was also man-powered), he could do crude navigation, and he could gather intelligence.
I would call him the first sub mariner, but that's me.