General Motors Electro-motive Division (EMD) built these early diesel engines. B&A's 700 was an E7, generally used for pulling passenger trains. B&A's 507 was an F3, specifically designed to have sufficient power to pull heavy freight trains. In the 1940's, when diesel engines first started to make their appearance on the nations railways, it was thought that while diesels were cleaner and easier to maintain, they would never have the power tp replace large steam engines such as B&A's Alcoa Mountain class locomotives (see MMN #14752. The F3 proved this assumption wrong and by 1960, virtually all of the nation's trains were pulled by diesel engines.