Nuclear Terrorism Conventions Implementation and Safety of Maritime Navigation Act of 2015

Nuclear Terrorism Conventions Implementation and Safety of Maritime Navigation Act of 2015 Amends the federal criminal code to provide that existing prohibitions against conduct that endangers the safe navigation of a ship: (1) shall apply to conduct that is committed against or on board a U.S. vessel or a vessel subject to U.S. jurisdiction, in U.S. territorial seas, or by a U.S. corporation or legal entity; and (2) shall not apply to activities of armed forces during an armed conflict or in the exercise of official duties. Sets forth procedures regarding the delivery of a person who is suspected of committing a maritime navigation or fixed platform offense to the authorities of a country that is a party to the Convention for the Suppression of Unlawful Acts against the Safety of Maritime Navigation. Subjects property used or intended to be used to commit or to facilitate the commission of a maritime navigation offense to civil forfeiture. Prohibits: (1) using in or on a ship or a maritime fixed platform any explosive or radioactive material, biological, chemical, or nuclear weapon, or other nuclear explosive device in a manner likely to cause death or serious injury or damage when the purpose is to intimidate a population or to compel a government or international organization to act or abstain from acting; (2) transporting on board a ship such material or device (or certain related material or technology) that is intended for such use, with specified exceptions; (3) transporting on board a ship a person known to have committed a maritime navigation offense intending to assist such person to evade prosecution; (4) injuring or killing any person in connection with such an offense; or (5) conspiring, attempting, or threatening to commit such an offense. Sets forth: (1) the circumstances in which the United States can exercise jurisdiction over such offenses, and (2) exceptions applicable to activities of the armed forces. Provides for civil forfeiture of property used to commit or to facilitate a violation. Prohibits anyone, knowingly, unlawfully, and with intent to cause death, serious bodily injury, or substantial damage to property or the environment, from: (1) possessing radioactive material or making or possessing a nuclear explosive device or a radioactive material dispersal or radiation-emitting device; (2) using radioactive material or a device, using, damaging, or interfering with the operation of a nuclear facility in a manner that causes or increases the risk of the release of radioactive material, or causing radioactive contamination or exposure to radiation; or (3) threatening, attempting, or conspiring to commit such an offense. Sets forth: (1) the circumstances in which the United States can exercise jurisdiction over such offenses, and (2) exceptions applicable to activities of the armed forces. Modifies the definition of "federal crime of terrorism" to include such offenses. Amends provisions prohibiting transactions involving nuclear materials to: (1) prohibit, intentionally and without lawful authority, carrying, sending, or moving nuclear material into or out of a country; and (2) establish an exception for activities of the armed forces.