1 standards, operating up to . History Amtrak ordered 15 HHP-8s in 1996 at the same time as its Acela Express trainsets. The HHP-8s have external styling that is similar to the Acela power cars, but are designed to operate as independent locomotives, hauling conventional passenger rolling stock. The units supplemented the EMD AEM-7s and allowed Amtrak to commence retirement of the GE E60. Amtrak did not purchase the locomotives outright but leased them from Philip Morris Capital. The locomotive's original type designation was HHL-8, for "High Horsepower Locomotive, 8,000 (nominal) horsepower". This was subsequently changed to HHP-8. In conjunction with the Amtrak order, MARC also acquired six HHP-8s, which MARC uses on their Penn Line service along the Northeast Corridor between Perryville and Washington, DC. Amtrak operated its HHP-8s on the Northeast Corridor between Boston and Washington, DC; racking up approximately 1,000,000 miles each in service (based on 2009 figure). In 2002, Amtrak's fleet of 15 units was temporarily withdrawn along with the Acela Express trains due to cracks in components of the trucks. Amtrak retirement Amtrak's HHP-8s suffered from low reliability. As a result, after only one decade in service, their replacement was considered, concurrent with the replacement of the older AEM-7 locomotive fleet, since a large order for a standardized fleet would have price economies, and the resultant fleet would have lower overall maintenance costs. A replacement fleet of 70 locomotives starting delivery in 2012 was planned, with HHP-8s kept as a reserve in the short term. In October 2010, Amtrak ordered 70 Siemens ACS-64 locomotives to replace both the HHP-8 and the older AEM-7 locomotives, with deliveries beginning in early 2013. Amtrak retired its last HHP-8 on November 7, 2014. All units are now stored; to avoid duplicate numbering with ACS-64 units 650–664, Amtrak renumbered its retired HHP-8s to 680–694. Philip Morris sued Amtrak in 2019, alleging that Amtrak had cannibalized eight of the fifteen locomotives for parts, in violation of the terms of the lease. The two parties settled the lawsuit in 2021; the terms were not disclosed. MARC refurbishment While reports in 2016 indicated that MARC planned to retire their HHP-8 locomotives and replace them with Siemens SC-44 Charger locomotives, MARC instead started a refurbishment program for its HHP-8s in 2017. Issues with equipment cooling that kept the HHP-8 locomotives from properly working were addressed. , the first HHP-8 reconditioned under this program had