In 1942, two creaking World War I–era U.S. destroyers in the Pacific fall through a temporal discontinuity into an alternate world—along with a Japanese battle cruiser—and find themselves fighting a very different World War II: This is the latest in the Destroyermen series (Rising Tides, 2011, etc.).
In this new world, the oceans swarm with gigantic, ferocious creatures. Warm-blooded dinosaurs evolved into the predatory "Grik," of whom only the leaders are truly intelligent—the rest follow programmed pack behavior. Fighting the Grik are intelligent cat-like "Lemurians," whom the Grik are attempting to exterminate. Further complicating the picture are two other human groups, the Empire of the New Britain Isles, descended from marooned British Royal Navy sailors from the 18th century, and the Holy Dominion, Spanish colonists who practice a bloodthirsty version of Catholicism involving human sacrifice, mostly of nubile young women. The Americans, led by Captain Matthew Reddy, ally themselves with the Lemurians and the Empire against the Grik and their Japanese collaborators, only to find themselves fighting the insensate Holy Dominion, too. The action, which rarely slackens, features splendid naval battles pitting destroyers against wooden-hulled fleets with cannons, land engagements where vastly outnumbered humans and Lemurians face hordes of vicious but none-too-bright dinosaurs, and inflexible Imperials terrorized by fanatically loyal Catholic armies. While some Japanese desert, unable to stomach the frightful Grik or the actions of their sadistic leaders, the Grik attempt to develop smarter, more flexible tactics and secret weapons. Intriguing what-ifs and convolutions by the boatload combine with churning, bloodthirsty warfare that grips despite the confusion of a largely indistinguishable cast of thousands struggling to the death in a historical melting pot amid re-named or unrecognizable landmarks.
Series fans will jump right in. Newcomers should begin at the beginning—and take notes.