The profession of arms is hard on hearing. The roar of engines, thunder of artillery, ear-splitting shrill of sirens, high hum of an engine room, jackhammering of weapons fire, piercing clang of metal on metal—even the joyful sound of instruments in a marching band—take a toll on the ears of members of the Canadian Armed Forces. Federal noise regulations consider hearing is safe at exposure to 87 decibels over an eight-hour workday, with the length of safe exposure time decreasing as decibels rise. Noise from artillery can reach 184 decibels. “Many weapons emit sounds that exceed the maximum achievable protection that double hearing protection can offer,” says a 2015 article in Military Medical Research. Inside fighter planes, the level can top 100 decibels. Even marching band members...