Which of the following is NOT a category of USNS ships?

The category that is not classified as a type of USNS (United States Naval Ship) is transport ships. The USNS primarily utilizes the following categories: Special Mission, Service Support, and Combat Logistics Force.

Special Mission ships are designed to support specific military operations, often equipped for unique purposes such as research, surveillance, or testing. Service Support ships provide essential logistics and repair services to naval operations, ensuring operational readiness. Combat Logistics Force ships play a critical role in providing logistical support to combat ships, including fuel, supplies, and equipment.

Transport ships, while essential in naval operations, do not specifically fall under the designated categories of USNS ships, which focus more on logistics, support, and mission-specific roles. Thus, this distinction makes transport ships the answer to the question.