to order sb to go to a place to deal with a difficult situation; to send sth by post / mail to a place where it will be dealt with
send sb in
to order sb to go to a place to deal with a difficult situation
Troops were sent in to restore order.
send sth in
to send sth by post / mail to a place where it will be dealt with
Have you sent in your application yet?
Definiciones del Oxford Advanced Learner's Dictionary, 9.ª edición