Military Standard 4023 (MIL-STD-4023) - High-altitude Electromagnetic Pulse (HEMP) Protection for Military Swface Ships is a new standard that establishes performance metrics, test protocols, and hardness margin levels for protection of military surface ships. It focuses on mission-critical ship systems that must function when subjected to the HEMP environment specified in MIL-STD-2 l 69C - High-altitude Electromagnetic Pulse (HEMP) Environment. MIL-STD-4023 is now an official DoD interface standard effective 25 January 2016. The Defense Threat Reduction Agency (DTRA) and the Naval Sea Systems Command (NAVSEA) authored this MIL-STD. This standard describes the activities to verify the protection design and maintain the hardness of a HEMP hardened ship such that mission critical capabilities are not degraded when exposed to the HEMP threat environment defined in MIL-STD-2169. It contains technical requirements, performance criteria, and test procedures for HEMP protection of military surface ships. The MIL-STD describes general and detailed requirements for the HEMP protection subsystem; EMP coupling and hardness allocation; analysis; equipment immunity testing; protective element performance testing; full ship verification testing; and hardness maintenance/surveillance testing. This paper summarizes the causes and damaging effects of HEMP threat environments; reviews the history of the Navy's precedent threat-level HEMP testing of ships; and provides DoD policy and near-term guidance to prepare for future threat-level testing of surface ship HEMP survivability in compliance with MIL­ STD-4023 . The best way to test a surface ship for high assurance of HEMP survivability is with a threat-level simulator. No other test or analytical assessment can effectively provide assurance that the ship will be able to complete its mission during and post HEMP events.