His letter is in complying with the War Power Resolution which requires the executive branch to notify Congress within 48 hours of American troop commitments.
"These personnel will support the operation of intelligence, surveillance, and reconnaissance aircraft for missions over northern Nigeria and the surrounding area," the president wrote. "The force will remain in Chad until its support in resolving the kidnapping situation is no longer required."
The Pentagon recently sent a team of eight experts to Chad to assist in the search by advising the Nigerian government on the recovery effort but President Obama has face criticism on the hill for not taking military action sooner.
Last week, Sen. John McCain, R-Arizona, said:
"We should devote more of our national capabilities to help our Nigerian partners in locating the girls. And if we get actionable intelligence about where they are being held, we should send U.S. Special Forces to rescue them –- with the approval and cooperation of the Nigerian government and security forces if possible, but without them if necessary."
The abduction of the girls occurred in mid-April and went largely unnoticed in global media until celebrities and the first lady took up the cause on Twitter with the #BringBackOurGirls hashtag campaign, bringing the situation into the global spotlight.