United States President-elect Donald Trump announce plans to nominate retired Marine General John Kelly to lead the Department of Homeland Security, a source familiar with the situation told Reuters on Wednesday, making him the third general sought for a high-level job in the new administration.

Kelly, 66, is the former head of the U.S. military’s Southern Command. The source said Trump was expected to name Kelly but did not elaborate.

The Republican president-elect, who has no military experience, also plans to nominate retired General James Mattis to lead the Department of Defense and picked retired Lieutenant General Michael Flynn to be his national security adviser.

Kelly differed with President Barack Obama on key issues and has warned of vulnerabilities along the United States’ southern border with Mexico.
As head of the U.S. Southern Command, his final leadership post in a 45-year military career, Kelly was responsible for U.S. military activities and relationships in Latin America and the Caribbean. He retired in January, 2016.

Although Kelly’s military experience may give him insight into overseas threats like drug trafficking or Islamist extremism, he would face new challenges at an agency that oversees everything from border security to protecting against cyber threats and responding to domestic crises.