The International Smelting & Refining Company became part of National Tunnel and Mines Company in 1937 at the end of the Great Depression. James Elton believed that consolidating would increase efficiency of local mining companies. He also wanted to build a tunnel under the Oquirrh Mountains to connect various mines. Elton planned for a tunnel 4.5 miles long that began north of the smelter and continued under the mountain. During the project, workers discovered a fissure under the mountain that prevented the tunnel from being completed. The failed, expensive tunnel project contributed to the bankruptcy of the company.
In World War II, the United States and her allies needed zinc to build weapons. Zinc could be processed from the slag (waste material of smelters) already at the smelter. So, the company added zinc-processing facilities. By this time, the smelter became an important asset to the mining industry because other regional smelters closed.
In 1948, Anaconda Copper, an international mining company specializing in copper, bought the smelter and railroad. Becoming part of Anaconda meant becoming more directly connected to the international mining industry. Anaconda began making changes, such as ending 24-hour railway services.