Hippo On The Move. In an unusual move, AMTK 608 (ACS-64) and 90691 (HHP-8/NPCU) were paired up on Train 43 (Pennsylvanian) out of New York Penn Station on the morning of Friday, January 13, 2023. The HHP-8 class were retired not long after the ACS-64 delivery was complete. This unit has been modified as an NPCU (Non Powered Control Unit) by Amtrak for possible future use on the railroad. The pair are seen passing through Harrison, New Jersey. The nickname "Hippo" comes from the shape of the engine as well as the HHP designation.