So the first podcast episode of A History of Submarines is out there – ‘Submersibles: The First Submarines’. And in it, there’s a mention of Roberto Valturio’s ‘De Re Militari’ (‘On The Military Arts’), first published in 1471(!). It is a compendium on military vehicles, weapons and how to use them.
Some real, some fantasy and imagination – like the submersible Valturio describes.
It was the second illustrated book ever to be printed in the Italian-speaking lands at the time. This by itself makes it pretty special. And we, now in 2021 when I’m writing this, can read it in all its glory thanks to modern technology (and, admittedly, international laws on the expiration of copyrights).
Granted, you’ll have to be up to speed on your Latin (the ‘f’ is an ‘s’ in the old Medieval spelling, by the way) but even if you’re not, it is an enticing read, if only for the drawings.

Such as the drawing above: the cigar-shaped submersible Valturio drew and which served as an inspiration for Leonardo da Vinci and his vision of a submersible.
Do give it a look-see! De re militari – Google Play
Interested in the episode on the first submersibles? Dive in here.