Borrowing text from Thomas Pynchon’s novel “Gravity’s Rainbow,” “Descent” purports to be a “visual journey across the theater of war.” Perhaps, but this oddly unaffecting film from Kevin Souls seems stuck in the over-covered rut of the nuclear age. This is certainly understandable to a degree. As horrific as flailing maces and bludgeoning battle axes were, charging knights battling on horseback never held the potential to completely destroy the planet. Rather than encompassing the specter of warfare in general, “Descent” instead seems to focus visually on those last few moments before an atomic blast; that morbid “what would you do if?” hypothetical question we asked ourselves about the same time we were trying to figure out how old we’d be when the year 2000 hit. Not surprisingly, the film is most chilling when the Bomb erupts in its awful display, set to the ironic sounds of “The Inkspots” singing “I Don’t Want to Set the World on Fire.” We haven’t, so far, and neither does this film.