Black project is an informal term used to describe a highly classified, top-secret military or defense project that is not publicly acknowledged by government, military personnel, or contractors.
In the United States, the formal term for a black project is an unacknowledged special access program (SAP).
The US depends on private defense contractors to develop and build military equipment.
The R&D department of Lockheed Martin is commonly referred to as Skunk Works; it is responsible for a number of aircraft designs, highly classified R&D programs, and exotic aircraft platforms.
Below are examples of previously unacknowledged black projects categorized per country.