“Fear the Walking Dead” is the spin-off to AMC’s smash-hit zombie apocalypse series, “The Walking Dead.” Since Season 4, the show has mostly followed “The Walking Dead” mainstay Morgan Jones (Lennie James) as he tries to establish a utopia in a fallen Texas.

Currently, “Fear the Walking Dead'” is airing its seventh season. When Season 7 premiered on Oct. 17, 2021, it picked up where Season 6 left off. Back then, Morgan’s nemesis, the cult leader Teddy (John Glover) and his followers managed to launch a nuclear missile from a beached submarine, in an attempt to wipe out all life on the planet (or, at least all life in Galveston, Texas, where the show currently takes place).

In Season 7, Morgan and his lover Grace (Karen David) are still eking out an existence in a zombie apocalypse that’s now also blanketed in nuclear radiation. In the second episode, “Six Hours,” Morgan and Grace take refuge in the same beached sub that launched the nuke. And when it comes to that particular element, viewers have a bone to pick — though thankfully, there might be a solid explanation for it.

Indeed, “Fear the Walking Dead” doesn’t bother explaining how and why the submarine is still working. But it actually makes sense if you know a little bit about submarines and how they work. On “Fear the Walking Dead,” the submarine’s official name is the  (SSBN-735). That “SSBN” designation makes the  an -class submarine, which carries nuclear ballistic missiles (via NTI.org). It’s also fueled by enriched uranium, just like all submarines deployed by the U.S. Navy have been since 1990 (via Atlas Obscura).