This report describes the technical design and outlines the expected performance of the Phase 1 Upgrade of the CMS Hadron Calorimeters. The upgrade is designed to improve the performance of the calorimeters at high luminosity with large numbers of pileup events by increasing the depth-segmentation of the calorimeter and providing new capabilities for anomalous background rejection. The photodetectors of the CMS Barrel and Endcap Hadron Calorimeters, currently hybrid photodiodes (HPDs), will be replaced by silicon photomultiplier (SiPM) devices. The single-channel phototubes of the Forward Hadron Calorimeter will be replaced by multi-anode phototubes operated in a dual-anode configuration. The readout electronics for all three calorimeter sy...