(1) Reduce, or prepare to reduce, the responsiveness or alert level of the intercontinental ballistic missiles of the United States. (2) Reduce, or prepare to reduce, the quantity of deployed intercontinental ballistic missiles of the United States to a number less than 400. (b) Exception The prohibition in subsection (a) shall not apply to any of the following activities: (1) The maintenance, sustainment, or replacement of intercontinental ballistic missiles. (2) Ensuring the safety, security, or reliability of intercontinental ballistic missiles. 1612. Sentinel intercontinental ballistic missile program silo activity The LGM–35A Sentinel intercontinental ballistic missile program shall refurbish and make operable not fewer than 150 silos for intercontinental ballistic missiles at each of the following locations: (1) Francis E. Warren Air Force Base, Laramie County, Wyoming. (2) Malmstrom Air Force Base, Cascade County, Montana. (3) Minot Air Force Base, Ward County, North Dakota. 1613. Matters relating to the acquisition and deployment of the Sentinel intercontinental ballistic missile weapon system (a) Authority for multi-year procurement Subject to section 3501 of title 10, United States Code, the Secretary of the Air Force may enter into one or more multi-year contracts for the procurement of up to 659 Sentinel intercontinental ballistic missiles and for subsystems associated with such missiles. (b) Authority for advance procurement The Secretary of the Air Force may enter into one or more contracts, beginning in fiscal year 2024, for advance procurement associated with the Sentinel intercontinental ballistic missiles for which authorization to enter into a multi-year procurement contract is provided under subsection (a), and for subsystems associated with such missiles in economic order quantities when cost savings are achievable. (c) Condition for out-year contract payments A contract entered into under subsection (a) shall provide that any obligation of the United States to make a payment under the