 Tankers and submarine chasers (usually called "sub-chasers") were built at the Riverside shipyard.The population of Duluth continued to grow in the postwar decade and a half, peaking at 107,884 in 1960.Economic decline began in the 1950s, when high-grade iron ore ran out on the Iron Range north of Duluth; ore shipments from the Duluth harbor had been critical to the city's economy.