The San Martin (サン・マルティン, San Marutin) is a Spanish stealth warship and the flagship of the Grande y Felicísima Armada, constructed for use in the Battle of Gravelines between Tres España and England. It appears like a regular Tres España ship, but its most distinctive feature is the giant cannon on top of it, which is able to fire a low-velocity bullet that can overwhelm the Musashi' gravity shields.
As experienced by Musashi, it is revealed that the San Martin has a total of three incarnations and using their stealth field in tandem with their unexpected numerical advantage, the San Martins are able to appear as only one ship, surprising their opponents by seeming to move impossible distances. However, they seem to have minor differences between one another, as Suzu Mukai was able to differentiate between them through her acute hearing.
- In the Battle of Gravelines, San Martin #3 is destroyed in a surprise attack on Musashi when Grace O'Malley of England takes the shot for Musashi with her ship and then rams her downed vessel into the stealth warship. San Martin #2 is shredded into pieces when it blocked the ether-boosted shot by Lypē Katathlipsē's Hyper Drive, protecting San Martin #1 to allow another shot at Musashi. San Martin #1 fails this shot when Mary uses her Excalibur Collbrande to cleave through not only the bullet, but the ship as well, putting it out of comission but not outright destroying it.