Defense planners develop vast network of tunnels and shelters as Moscow plans war games Russia is planning its biggest military exercise in years, and its neighbor Finland is going underground. A subterranean city beneath Helsinki forms a crucial line of defense for the capital. Finnish soldiers routinely train here, with a mission to keep Finland’s government running and city residents safe in a network that features more than 124 miles of tunnels, passageways and shelters. Much of the network has been adapted over recent decades with defense in mind. Blast doors seal entrances. Passageways are adapted so the military—with a regiment dedicated to controlling the tunnels—can contain enemy infiltrators. Utility and subway tunnels provide arteries for communications, water supply and Wi-Fi. There…