Bombardier Transportation signed a frame contract with Berliner Verkehrsbetriebe (BVG) for the delivery of 24 4-car units (Series HK) to operate on Berlin's small profile network. Four pre-series trains have been in operation at BVG since the middle of 2001. The delivery of all the vehicles was completed at the end of 2007 with the supply of the last train.
With electronically operated doors and wide passageways, these low-weight aluminium vehicles are designed for optimal passenger flow and economic service. Two units are usually operated together and can transport up to 650 people despite the compact vehicle dimensions. A light and airy design contributes to the comfortable and secure passenger environment. An air cooled propulsion system with IGBT technology provides the required 1MW of power per unit. The MITRAC train communication and control system coordinates all vehicle functions and provides the driver with a detailed train status and diagnostic display.