In the Army, the Head of the Agency is the Secretary of the Army. However, via General Order #3, the Secretary delegates responsibility and authority to the Assistant Secretary of the Army (Acquisition, Logistics and Technology) to act as the agency head for all acquisition matters.
The responsibility and authority of the Senior Procurement Executive also follows this same line of delegation. Ms. Heidi Shyu currently serves as the Acting Assistant Secretary of the Army for Acquisition, Logistics and technology, and in that capacity, she is the Senior Procurement Executive and Agency Head. There is only one Senior Procurement Executive in the Army (as well as in each Federal Agency).