A Marine fires an M777A2 howitzer in the early morning in Syria, Saturday, June 3. Marines have been conducting 24-hour all-weather fire support for the coalition's local partners, the Syrian Democratic Forces. It's to support Combined Joint Task Force Operation Inherent Resolve. Marine Corps photo by Sgt. Matthew Callahan. Sgt. Matthew Callahan

A Russian jet comes within a few feet of a U.S. Air Force reconnaissance jet over the Baltic Sea on June 19 in a maneuver that has been criticized as unsafe. The photo shows the Russian SU-27 in the background, and the wing of the U.S. RC-135U in the foreground. Master Sgt. Charles Larkin Sr/AP

U.S. Marine candidates participate in events, such as the obstacle, endurance and combat courses, at the Officer Candidate School, Marine Corps Base Quantico, in Virginia, on June 14. Candidates must go through three months of intensive training to determine if they have the leadership, moral, mental, and physical qualities required to be a U.S. Marine Corps officer. Lance Cpl. Cristian Ricardo/MCB Quantico Combat Ca

Army engineers conduct demolition training in Bemowo Piskie, Poland, Thursday, June 8. The training is part of Saber Strike 17, a multinational initiative of the U.S. Army designed to enhance the NATO alliance throughout the Baltic region and Poland. Courtesy Sgt. Justin Geiger

Lance Cpl. Bando Camposvilla jumps from a ten foot high tower during annual swim qualification aboard Camp Hansen, Okinawa, Japan, on June 25. The Marines complete their swim qualification to build confidence and increase survivability in the water. Cpl. Aaron Patterson/Marine Corps Base Hawaii

Ninety-two year old Charles Norman Shay, a Native American D-Day veteran, salutes during the National Anthem at the International Commemorative Ceremony of the Allied Landing in Normandy at Utah Beach. NurPhoto/Getty Images

Soldiers aboard a U.S. Air Force CH-47 Chinook helicopter take part in the NATO military exercise 'Iron Wolf 2017' at a training range in Pabrade, Lithuania on June 22. The exercise, being held in different parts of Lithuania, will involve roughly 5,000 participants from Lithuania and nine other NATO allies. Mindaugas Kulbis/AP

A Kyodo News helicopter shows the damaged part of the U.S. Navy's guided-missile destroyer, the USS Fitzgerald, which collided with a Filipino container vessel off Yokosuka, south of Tokyo. The accident has left seven crew members of the destroyer unaccounted for and three injured. Kyodo News/Getty Images

Tramanh Best clutches a picture of her father, Army veteran Ricky Best, as she stands with her family during his committal service at Willamette National Cemetery on June 5 in Portland, Oregon. Best, 53, and Taliesin Namkai-Meche, 23, were stabbed to death and Micah Fletcher, 21, was severely injured aboard a commuter train after they tried to stop Jeremy Christian from harassing two teenage girls, one of whom was wearing a hijab, with racist taunts. Scott Olson/Getty Images

U.S. Coast Guard Academy cadet Ryan Brumm shouts at members of Whiskey Two swab company as they march into the wardroom for lunch on June 26 in New London, Connecticut SEAN D. ELLIOT/AP

Cadets climb the rigging while preparing to set sail aboard the US Coast Guard Eagle during the Parade of Sail at Sail Boston on Saturday, June 17. The Eagle led the flotilla around the Boston Harbor. Boston Globe/Getty Images

Navy Petty Officer 2nd Class Sean Morin fights off a simulated attacker after being exposed to oleoresin capsicum, or pepper spray, as part of security training in Yokosuka, Japan, on June 23. MC3 Dylan McKay

A US soldier advising Iraqi forces is seen in the city of Mosul during the ongoing offensive by Iraqi troops to retake the last district still held by the Islamic State (IS) group. MOHAMED EL-SHAHED/Getty Images

Lt. Gen. Paul E. Funk II led a group during a D-Day observance on June 6, to mark the 73rd anniversary of the momentous Allied assault on the beaches of Normandy. The event featured a run and obstacle course at the Phantom Warrior Air Assault Course, focusing on the service and sacrifices of "The Greatest Generation." US Army

A Marine participates in an advanced water survival course at Camp Pendleton, California, on June 14. The course focused on strengthening individual Marines' self-preservation and rescue skills in water. Sgt. Rodion Zabolotniy

A member of the US Marine Corps stands guard outside the West Wing of the White House while US President Donald Trump works on June 6. BRENDAN SMIALOWSKI/Getty Images

President Donald Trump, center, is seen looking out of the window of Marine One on its approach to the South Lawn of the White House in Washington, D.C. on June 13. Pablo Martinez Monsivais/AP

The crew of the USS Gabrielle Giffords stands at the ready prior to the commissioning ceremony on Saturday, June 10, in Galveston, Texas. The U.S. Navy commissioned the warship, which is named for former Rep. Gabrielle Giffords (D-AZ.), a gun violence survivor. It's the third Navy ship ever to be named after a living woman. Daniel Kramer/Getty Images