Sen. Scott Brown (R-Mass.) is headed to Afghanistan. ((Melina Mara/The Washington Post))

Massachusetts Republican Sen. Scott Brown made a surprising announcement today: He’s going to Afghanistan as part of his service as a lieutenant colonel in the Massachusetts Army National Guard. He requested to do his annual two weeks of training there.

“Following in the tradition of other lawmakers who have completed their military service requirements overseas, this year I have requested to conduct my annual training in Afghanistan,” he said in a statement. “Doing so will help me to better understand our ongoing mission in that country, and provide me first-hand experience for my duties on the Senate Armed Services, Homeland Security, and Veterans Affairs committees.”

It’s rare for a member of Congress to serve in the reserves or National Guard, and even rarer for one to serve overseas while in office. Brown is one of only three senators in the National Guard or Army and Navy reserves; Mark Kirk (R-Ill.) and Lindsey Graham (R-N.C.) are the other two. Five lawmakers in the House are members.

Under a 1999 Department of Defense directive, members of Congress in the armed forces are automatically transferred to standby or retired reserve status during wartime. In 2006, Graham became the first sitting member of Congress in decades to perform military duties in a war zone. The Air Force Reserve colonel went to Afghanistan to train judges, lawyers and prosecutors.

“Senator Brown takes very seriously his membership in the National Guard,” said Eric Fehrnstrom, an adviser to the senator. “He's been performing military service for more than 30 years, and it's not something he was willing to give up even after his election to the U.S. Senate.”

Brown has been in the National Guard since 1979, but this will be his first deployment to a war zone. He is up for re-election to a full six-year term in 2012 and is a major Democratic target.