​For DoD, a written acquisition plan is required for--

(A) Acquisitions for development, as defined in FAR 35.001, when the total cost of all contracts for the acquisition program is estimated at $10 million or more;
 
(B) Acquisitions for production or services when the total cost of all contracts for the acquisition program is estimated at $50 million or more for all years or $25 million or more for any fiscal year; and
 
(C) Any other acquisition considered appropriate by the department or agency.
 
[DFARS 207.103(d)(i)]
Note that the DFARS deviates from FAR 7.103(e), which requires written acquisition plans for all contracts that are not firm-fixed-price.