This engine (1 of 42 class B units) was built by the company's Altoona Works division in 1934 specifically for switching. Unlike most electric switchers which had two axles, the B class were three axle applying a total of 1,710 hp to the rail. Some early sets were semi-permanently connected together and referred as BB-1's. A later version version was developed to operate on outside third rail with small pantographs on the roof and were known as Class BB2. BB3 were actually individual units joined with standard couplers and the usual cables. #5690 is a B1 class designed to operate as a single unit. Top speed was claimed to have been 25 mph though they rarely exceeded 5 mph.