1.
If you send in something such as a competition entry or a letter applying for a job, you post it to the organization concerned.
Applicants are asked to send in a CV and a covering letter...
PHRASAL VERB : V P n (not pron) , also V n P
2.
When a government sends in troops or police officers, it orders them to deal with a crisis or problem somewhere.
He has asked the government to send in troops to end the fighting.
PHRASAL VERB : V P n (not pron) , also V n P