secret service; intelligence agency
Generic use for a government intelligence or security agency, especially one referred to with an English-style name.
He belongs to the secret service of a certain country.
the U.S. Secret Service
Specific use for the United States Secret Service; context such as アメリカの often makes this sense clear.
The U.S. Secret Service protects the president.
The Secret Service is guarding the president.
He joined the Secret Service after graduating from college.