; and (B) an objective value indicating the lowest cost expected to be achieved for that category, as determined by the Secretary concerned. (2) Cost categories specified The cost categories specified in this paragraph are the following: (A) Unit recurring flyaway cost. (B) Average procurement unit cost. (C) Gross/weapon system unit cost. (D) Aircraft cost-per-tail-per-year. (E) Aircraft cost-per-flight-hour. (f) Definitions In this section, the term Secretary concerned means— (1) the Secretary of the Navy, with respect to aircraft programs of the Navy and the Marine Corps; and (2) the Secretary of the Air Force, with respect to aircraft programs of the Air Force. 225. Continuous capability development and delivery program for F–35 aircraft (a) Designation of major subprogram In accordance with section 4203 of title 10, United States Code, the Secretary of Defense shall designate all Block 4 and Technical Refresh–3 elements of the F–35 aircraft acquisition program, collectively, as a single major subprogram of the F–35 aircraft acquisition program. (b) Procurement of F–35 developmental testing aircraft (1) In general From the aircraft described in paragraph (2), the Program Executive Officer for the F–35 aircraft program shall designate two F–35A aircraft, two F–35B aircraft, and two F–35C aircraft to be manufactured and delivered, by not later than the end of 2030, in a necessary configuration that would adequately support future F–35 developmental testing activities. (2) Aircraft described The aircraft described in this paragraph are F–35 aircraft to be procured— (A) as part of the Lot 19 production lot or a subsequent production lot for F–35 aircraft