black operation
type of covert operation by a government agency, military or paramilitary organization, involving enhanced secrecy due to its sensitive nature. This may be caused by a partly illegal or unethical nature of the operation.
en-GB/ˈblæk ˌɒpəˈɹeɪʃən/
en-US/ˈblæk ˌɑpɚˈeɪʃən/