Chairman of the Joint Chiefs of Staff U.S. Army General Martin Dempsey (L) and U.S. Defense Secretary Ash Carter (R) stand for the arrival of President Barack Obama for the Memorial Day observance at Arlington National Cemetery in Arlington, Virginia May 25, 2015. REUTERS/Jonathan Ernst 

U.S. Defense Secretary Ash Carter (L) and Chairman of the Joint Chiefs of Staff General Martin Dempsey hold a joint news conference at the Pentagon in Washington May 7, 2015. REUTERS/Yuri Gripas 

U.S. Defense Secretary Ash Carter (L) and Chairman of the Joint Chiefs of Staff General Martin Dempsey hold a joint news conference at the Pentagon in Washington May 7, 2015. REUTERS/Yuri Gripas 

U.S. Defense Secretary Ash Carter (L) and Chairman of the Joint Chiefs of Staff General Martin Dempsey hold a joint news conference at the Pentagon in Washington May 7, 2015. REUTERS/Yuri Gripas 

U.S. Defense Secretary Ash Carter (L) applauds outgoing Chairman of the Joint Chiefs of Staff General Martin Dempsey at their joint news conference at the Pentagon in Washington May 7, 2015. REUTERS/Yuri Gripas TPX IMAGES OF THE DAY

U.S. Defense Secretary Ash Carter (L) and Chairman of the Joint Chiefs of Staff General Martin Dempsey arrive at a joint news conference at the Pentagon in Washington May 7, 2015. REUTERS/Yuri Gripas 

U.S. Defense Secretary Ash Carter (L) and Chairman of the Joint Chiefs of Staff General Martin Dempsey hold a joint news conference at the Pentagon in Washington May 7, 2015. REUTERS/Yuri Gripas 

United States Secretary of Defense Ash Carter (R) listens to Joint Chiefs of Staff Chairman U.S. Army General Martin Dempsey (L) testify before a Senate Appropriations Defense subcommittee hearing on the defense budget on Capitol Hill in Washington May 6, 2015. REUTERS/Gary Cameron

Joint Chiefs of Staff Chairman U.S. Army General Martin Dempsey (L) testifies before a Senate Appropriations Defense subcommittee hearing on the defense budget on Capitol Hill in Washington May 6, 2015. Dempsey will leave his post in October of this year. U.S. Secretary of Defense Ash Carter listens at right. REUTERS/Gary Cameron

Joint Chiefs of Staff Chairman U.S. Army General Martin Dempsey testifies before a Senate Appropriations Defense subcommittee hearing on the defense budget on Capitol Hill in Washington May 6, 2015. Dempsey will leave his post in October of this year. REUTERS/Gary Cameron

Joint Chiefs of Staff Chairman U.S. Army General Martin Dempsey listens to opening remarks before a Senate Appropriations Defense subcommittee hearing on the defense budget on Capitol Hill in Washington May 6, 2015. Dempsey will leave his post this October. REUTERS/Gary Cameron

Joint Chiefs of Staff Chairman U.S. Army General Martin Dempsey (R) talks to an aide ahead of testifying before a Senate Appropriations Defense subcommittee hearing on the defense budget on Capitol Hill in Washington May 6, 2015. REUTERS/Gary Cameron

United States Secretary of Defense Ash Carter (L) and Joint Chiefs of Staff Chairman U.S. Army General Martin Dempsey (R) arrive to testify before a Senate Appropriations Defense subcommittee hearing on the defense budget on Capitol Hill in Washington May 6, 2015. REUTERS/Gary Cameron

United States Secretary of Defense Ash Carter (R) listens to Joint Chiefs of Staff Chairman U.S. Army General Martin Dempsey testify before a Senate Appropriations Defense subcommittee hearing on the defense budget on Capitol Hill in Washington May 6, 2015. REUTERS/Gary Cameron

United States Secretary of Defense Ash Carter (L) and Joint Chiefs of Staff Chairman U.S. Army General Martin Dempsey (2nd L) greet Senator Thad Cochran (R-MS) (2nd R) and Senator Richard Shelby (R-AL), before a Senate Appropriations Defense subcommittee hearing on the defense budget on Capitol Hill in Washington May 6, 2015. REUTERS/Gary Cameron

U.S. Secretary of Defense Ashton Carter (front), and Chairman of the Joint Chiefs General Martin Dempsey (rear), enter the Pentagon briefing room to speak with reporters at the Pentagon in Washington April 16, 2015. REUTERS/James Lawler Duggan 

Chairman of the Joint Chiefs General Martin Dempsey speaks to reporters at the Pentagon in Washington April 16, 2015. REUTERS/James Lawler Duggan 

U.S. Secretary of Defense Ashton Carter (R) and Chairman of the Joint Chiefs General Martin Dempsey speak to reporters at the Pentagon in Washington April 16, 2015. REUTERS/James Lawler Duggan 

U.S. Secretary of Defense Ashton Carter (R) and Chairman of the Joint Chiefs General Martin Dempsey speak to reporters at the Pentagon in Washington April 16, 2015. REUTERS/James Lawler Duggan 

U.S. Secretary of Defense Ashton Carter (R) and Chairman of the Joint Chiefs General Martin Dempsey speak to reporters at the Pentagon in Washington April 16, 2015. REUTERS/James Lawler Duggan 

U.S. Secretary of Defense Ashton Carter and Chairman of the Joint Chiefs General Martin Dempsey (not pictured) speak to reporters at the Pentagon in Washington April 16, 2015. REUTERS/James Lawler Duggan 

U.S. Secretary of Defense Ashton Carter (R) and Chairman of the Joint Chiefs General Martin Dempsey speak to reporters at the Pentagon in Washington April 16, 2015. REUTERS/James Lawler Duggan 

U.S. Secretary of Defense Ashton Carter and Chairman of the Joint Chiefs General Martin Dempsey speak to reporters at the Pentagon in Washington April 16, 2015. REUTERS/James Lawler Duggan 

U.S. Secretary of Defense Ashton Carter and Chairman of the Joint Chiefs General Martin Dempsey (not pictured) speak to reporters at the Pentagon in Washington April 16, 2015. REUTERS/James Lawler Duggan 

South Korean Defence Minister Han Min-Koo (R) talks with U.S. General Martin Dempsey (L), chairman of the U.S. Joint Chiefs of Staff, during their meeting at the Defence Ministry in Seoul on March 27, 2015. REUTERS/Jing Yeon-Je/Pool 

South Korean Defence Minister Han Min-Koo (R) shakes hands with U.S. General Martin Dempsey (L), chairman of the U.S. Joint Chiefs of Staff, during their meeting at the Defence Ministry in Seoul on March 27, 2015. REUTERS/Jing Yeon-Je/Pool 

South Korean Defence Minister Han Min-Koo (R) shakes hands with U.S. General Martin Dempsey (L), chairman of the U.S. Joint Chiefs of Staff, during their meeting at the Defence Ministry in Seoul March 27, 2015. REUTERS/Jung Yeon-Je/Pool 

U.S. Army General Martin Dempsey, chairman of the Joint Chiefs of Staff, and his South Korean counterpart Admiral Choi Yun-hee (obscured) inspect South Korean Honour Guards during a welcoming ceremony at the Joint Chiefs of Staff in Seoul March 27, 2015. REUTERS/Kim Hong-Ji 

U.S. Army General Martin Dempsey (R), chairman of the Joint Chiefs of Staff, and his South Korean counterpart Admiral Choi Yun-hee inspect South Korean Honour Guards during a welcoming ceremony at the Joint Chiefs of Staff in Seoul March 27, 2015. REUTERS/Kim Hong-Ji 

U.S. Army General Martin Dempsey (3rd L), chairman of the Joint Chiefs of Staff, and his South Korean counterpart Admiral Choi Yun-hee (2nd L) leave after a welcoming ceremony at the Joint Chiefs of Staff in Seoul March 27, 2015. REUTERS/Kim Hong-Ji 

U.S. Army General Martin Dempsey (R), chairman of the Joint Chiefs of Staff, and his South Korean counterpart Admiral Choi Yun-hee arrive at a welcoming ceremony at the Joint Chiefs of Staff in Seoul March 27, 2015. REUTERS/Kim Hong-Ji 

U.S. Army General Martin Dempsey (L), chairman of the Joint Chiefs of Staff, salutes with his South Korean counterpart Admiral Choi Yun-hee during a welcoming ceremony at the Joint Chiefs of Staff in Seoul March 27, 2015. REUTERS/Kim Hong-Ji 

U.S. Army General Martin Dempsey (L), chairman of the Joint Chiefs of Staff, meets with Japan's Prime Minister Shinzo Abe (R) at Abe's official residence in Tokyo March 25, 2015. REUTERS/Franck Robichon/Pool 

U.S. Army General Martin Dempsey (L), chairman of the Joint Chiefs of Staff, meets with Japan's Prime Minister Shinzo Abe (R) at Abe's official residence in Tokyo March 25, 2015. REUTERS/Franck Robichon/Pool 

U.S. Army General Martin Dempsey (L), chairman of the Joint Chiefs of Staff, shakes hands with Japan's Prime Minister Shinzo Abe at the start of their talks at Abe's official residence in Tokyo March 25, 2015. REUTERS/Franck Robichon/Pool 

U.S. Army General Martin Dempsey (L), chairman of the Joint Chiefs of Staff, shakes hands with Japan's Prime Minister Shinzo Abe at the start of their talks at Abe's official residence in Tokyo March 25, 2015. REUTERS/Franck Robichon/Pool 

Members of Japan's Self-Defence Force's honour guard prepare for a ceremony for U.S. Army General Martin Dempsey, chairman of the Joint Chiefs of Staff, at the Defense Ministry in Tokyo March 25, 2015. REUTERS/Toru Hanai

Members of Japan's Self-Defence Force's honour guard prepare for a ceremony for U.S. Army General Martin Dempsey, chairman of the Joint Chiefs of Staff, at the Defense Ministry in Tokyo March 25, 2015. REUTERS/Toru Hanai
TPX IMAGES OF THE DAY

U.S. Army General Martin Dempsey (L), chairman of the Joint Chiefs of Staff, shakes hands with Japan's Defense Minister Gen Nakatani during their meeting at the Defense Ministry in Tokyo March 25, 2015. REUTERS/Toru Hanai

U.S. Army General Martin Dempsey (L), chairman of the Joint Chiefs of Staff, shakes hands with Japan's Defense Minister Gen Nakatani during their meeting at the Defense Ministry in Tokyo March 25, 2015. REUTERS/Toru Hanai

U.S. Army General Martin Dempsey (L), chairman of the Joint Chiefs of Staff, shakes hands with Admiral Katsutoshi Kawano, chief of the Japanese Self-Defense Forces' Joint Staff, during their meeting at the Defense Ministry in Tokyo March 25, 2015. REUTERS/Toru Hanai

U.S. Army General Martin Dempsey (front R), chairman of the Joint Chiefs of Staff, reviews honor guards with Admiral Katsutoshi Kawano (front L), chief of the Japanese Self-Defense Forces' Joint Staff, at the Defense Ministry in Tokyo March 25, 2015. REUTERS/Toru Hanai

U.S. Army General Martin Dempsey, chairman of the Joint Chiefs of Staff, reviews honor guards at the Defense Ministry in Tokyo March 25, 2015. REUTERS/Toru Hanai

U.S. Army General Martin Dempsey, chairman of the Joint Chiefs of Staff, reviews honor guards at the Defense Ministry in Tokyo March 25, 2015. REUTERS/Toru Hanai

U.S. Army General Martin Dempsey (C), Chairman of the Joint Chiefs of Staff, reviews honor guards at the Defense Ministry in Tokyo March 25, 2015. REUTERS/Toru Hanai

U.S. Army General Martin Dempsey, Chairman of the Joint Chiefs of Staff, salutes as he reviews honor guards at the Defense Ministry in Tokyo March 25, 2015. REUTERS/Toru Hanai

Chairman of the Joint Chiefs of Staff Army Gen. Martin Dempsey (L), U.S. Defense Secretary Ash Carter (C) and Secretary of State John Kerry testify at a Senate Foreign Relations Committee hearing on "The President's Request for Authorization to Use Force Against ISIS: Military and Diplomatic Efforts"
on Capitol Hill in Washington March 11, 2015.
REUTERS/Kevin Lamarque (UNITED STATES - Tags: POLITICS MILITARY) 

U.S. Secretary of State John Kerry (R) speaks during a Senate Foreign Relations Committee hearing on "The President's Request for Authorization to Use Force Against ISIS: Military and Diplomatic Efforts" on Capitol Hill in Washington March 11, 2015. With Kerry are U.S. Defense Secretary Ash Carter (C) and Chairman of the Joint Chiefs of Staff Army Gen. Martin Dempsey.
REUTERS/Kevin Lamarque (UNITED STATES - Tags: POLITICS MILITARY) 

U.S. Secretary of State John Kerry (R) speaks during a Senate Foreign Relations Committee hearing on "The President's Request for Authorization to Use Force Against ISIS: Military and Diplomatic Efforts" on Capitol Hill in Washington March 11, 2015. With Kerry are U.S. Secretary of Defense Ash Carter (C) and Chairman of the Joint Chiefs of Staff Army Gen. Martin Dempsey (L).
REUTERS/Kevin Lamarque (UNITED STATES - Tags: POLITICS MILITARY) 

U.S. Secretary of Defense Ash Carter takes his seat to testify at a Senate Foreign Relations Committee hearing on "The President's Request for Authorization to Use Force Against ISIS: Military and Diplomatic Efforts"
on Capitol Hill in Washington March 11, 2015. Beside him is Chairman of the Joint Chiefs of Staff Army Gen. Martin Dempsey.
REUTERS/Kevin Lamarque (UNITED STATES - Tags: POLITICS MILITARY) 

Joint Chiefs of Staff Chairman Army Gen. Martin Dempsey (L), U.S. Defense Secretary Ash Carter (C) and Secretary of State John Kerry testify at a Senate Foreign Relations Committee hearing on "The President's Request for Authorization to Use Force Against ISIS: Military and Diplomatic Efforts"
on Capitol Hill in Washington March 11, 2015.
REUTERS/Kevin Lamarque (UNITED STATES - Tags: POLITICS MILITARY) 

U.S. Chairman of the Joint Chiefs of Staff Army General Martin Dempsey (L), Defense Secretary Ash Carter (C) and Secretary of State John Kerry testify at a Senate Foreign Relations Committee hearing on "The President's Request for Authorization to Use Force Against ISIS: Military and Diplomatic Efforts"
on Capitol Hill in Washington March 11, 2015.
REUTERS/Kevin Lamarque (UNITED STATES - Tags: POLITICS MILITARY) 

U.S. Army General Martin Dempsey (L) speaks during a news conference with Iraq's Defence Minister Khaled al-Obeidi in Baghdad March 9, 2015. Dempsey, the top U.S. military officer, said on Monday that Islamic State would be defeated, as he visited Baghdad during an offensive against the radical insurgents which has seen Washington's military role overshadowed by Iran. REUTERS/Ahmed Saad (IRAQ - Tags: POLITICS MILITARY CONFLICT CIVIL UNREST) 

U.S. Army General Martin Dempsey (L) speaks during a news conference with Iraq's Defence Minister Khaled al-Obeidi in Baghdad March 9, 2015. Dempsey, the top U.S. military officer, said on Monday that Islamic State would be defeated, as he visited Baghdad during an offensive against the radical insurgents which has seen Washington's military role overshadowed by Iran. REUTERS/Ahmed Saad (IRAQ - Tags: POLITICS MILITARY CONFLICT CIVIL UNREST) 

U.S. Army General Martin Dempsey (L) gestures during a news conference with Iraq's Defence Minister Khaled al-Obeidi in Baghdad March 9, 2015. Dempsey, the top U.S. military officer, said on Monday that Islamic State would be defeated, as he visited Baghdad during an offensive against the radical insurgents which has seen Washington's military role overshadowed by Iran. REUTERS/Ahmed Saad (IRAQ - Tags: POLITICS CIVIL UNREST CONFLICT MILITARY) 

Iraq's Defence Minister Khaled al-Obeidi speaks during a news conference in Baghdad March 9, 2015. Chairman of the U.S. Joint Chiefs of Staff General Martin Dempsey held talks with Obeidi while Iraqi troops and mainly Shi'ite Muslim militia backed by Iran battled to retake the city of Tikrit from the Islamic State. REUTERS/Ahmed Saad (IRAQ - Tags: POLITICS CIVIL UNREST MILITARY CONFLICT HEADSHOT) 

U.S. Army General Martin Dempsey speaks during a news conference in Baghdad March 9, 2015. Dempsey , the top U.S. military officer, said on Monday that Islamic State would be defeated, as he visited Baghdad during an offensive against the radical insurgents which has seen Washington's military role overshadowed by Iran. REUTERS/Ahmed Saad (IRAQ - Tags: POLITICS CONFLICT CIVIL UNREST MILITARY) 

Iraq's Defence Minister Khaled al-Obeidi (R) speaks during a news conference with U.S. Army General Martin Dempsey in Baghdad March 9, 2015. Dempsey, the top U.S. military officer, said on Monday that Islamic State would be defeated, as he visited Baghdad during an offensive against the radical insurgents which has seen Washington's military role overshadowed by Iran. REUTERS/Ahmed Saad (IRAQ - Tags: POLITICS MILITARY CIVIL UNREST CONFLICT) 

U.S. Army General Martin Dempsey speaks during a news conference in Baghdad March 9, 2015. Dempsey , the top U.S. military officer, said on Monday that Islamic State would be defeated, as he visited Baghdad during an offensive against the radical insurgents which has seen Washington's military role overshadowed by Iran. REUTERS/Ahmed Saad (IRAQ - Tags: POLITICS CONFLICT CIVIL UNREST) 

U.S. Army General Martin Dempsey (L) speaks during news conference with Iraq's Defence Minister Khaled al-Obeidi in Baghdad March 9, 2015. REUTERS/Ahmed Saad (IRAQ - Tags: POLITICS CIVIL UNREST CONFLICT)