BVG Class HKThe BVG Class HK is a type of electric multiple unit in service on the Berlin U-Bahn. It is operated by Berliner Verkehrsbetriebe . The HK is a Kleinprofil variant of the larger Großprofil H series.Production historyIn the early 2000s, Berliner Verkehrsbetriebe ordered twenty four-car small-profile HK class trains from Bombardier Transportation. Four pre-production trains underwent trial service for three years before being fully adopted. The completed trains were delivered to Berliner Verkehrsbetriebe between mid-2006 and the end of 2007. The vehicle bodies feature aluminum shells, with modular roof, cab, and underframe components. The power draw of the HK variant is 1,020 kW as compared to the larger H series 2,160 kW.Operational historyThe HK series primarily operates on the U2 line.