Do I need the word “the”?
I want to build a career with the Japan Transport Department.
Japan Transport Department is name.
In BrE, we usually add "the" even if it's not officially part of the name.
I used to work for the United Kingdom Intelligence Service.
I want to have a career in/with the French Immigration Department.
Some departments use the noun for the name of the country (United Kingdom) and some use the adjective, which usually matches the word for the nationality (French).