TNT's The Last Ship will indeed end with Season 5

Deadline

TNT and TBS president Kevin Reilly confirms The Last Ship will end with Season 5. Last fall, cast member Travis Van Winkle let slip the news when he reminisced on Instagram about wrapping the show in a post he later deleted. At the time, TNT said, "we greenlit the fifth with the idea that it could be the final season, however it’s far too early to make that determination.”