This Early Feasibility Study (EFS) protocol describes the clinical study requirements for the Relay Branch System; a device designed to provide an option for patients with arch and proximal descending chronic thoracic aortic pathologies. As an EFS, this investigation is intended to provide proof of principle and initial clinical safety data on the Relay Branch System. The study is planned as an initial investigation of the device for aortic arch and proximal descending thoracic aortic aneurysmal disease, PAU (including IMH) and uncomplicated chronic Type B aortic dissection (including IMH). The study will yield information on procedural techniques; assessing the safety and effectiveness of the device at the index procedure and at 30 days, focusing on device delivery and deployment, and circulatory exclusion of the pathologic process. As a branched device, patency of the endograft branches will also be assessed.