The Ship in the Woods (Viking Saga, #3)

Swedish Vikings founded Russia and named the realm after their leader, Rurik. A thousand years later, during the Cold War, Swedish archeologists raised the Vasa, a mighty gunship that had been meant to seal Sweden's second claim as a world power. The Ship in the Woods follows two timelines -- the Vikings venturing out from Sweden to besiege Constantinople, and the 1960s archeologists unearthing clues from Cold War spies about what seems might be the end of the world.