Arlington services contractor PAE is set to acquire A-T Solutions, a defense and national security contractor based in Tysons Corner, for an undisclosed sum, the company said Thursday.

This is PAE’s second acquisition this year, and its latest in the national security sector. PAE bought the Global Security and Solutions unit of Falls Church-based U.S. Investigations Services in January and created a new unit named PAE National Security Solutions as a result.

The purchase of A-T, a contractor that specializes in counterterrorism work for the Pentagon, intelligence agencies and the Department of Homeland Security, gives PAE access to employees with high-level security clearances, which was also the rationale for its purchase of the USIS unit earlier this year.

“In the 13 years since its founding, A-T Solutions has grown into an internationally recognized leader in the defense and national security industry, and this team is trusted by over 200 government customers to provide highly specialized counter-threat services,” PAE chief executive John Heller said in a statement.

The company was spun off from defense giant Lockheed Martin in 2011 and is currently owned by Lindsay Goldberg, a private-equity firm.

A-T Solutions has more than 700 employees, many of whom are based in Northern Virginia. It is owned by private equity firms CI Capital and CoVant.

The transaction is expected to close at the end of May.