The medal is approved only for operations "in which no other United States service medal is approved," according to the Defense Department. It's awarded to service members who, as a unit, participate in a U.S. military operation "deemed to be a significant activity and who encounter no foreign armed opposition or imminent hostile action."

Thousands of U.S. service members who've been sent to operate along the Mexico border will receive a military award reserved for troops who "encounter no foreign armed opposition or imminent hostile action."

The Pentagon has authorized troops who have deployed to the border to assist U.S. Customs and Border Protection (CBP) since last April to receive the Armed Forces Service Medal. Details about the decision were included in a Marine Corps administrative message in response to authorization from the Defense Department.

There is no end date for the award since the operation remains ongoing.

"The Under Secretary of Defense has authorized the Armed Forces Service Medal to service members who have provided support to CBP, starting from April 7, 2018 [until a date to be determined]," said Army Lt. Col. Chris Mitchell, a Defense Department spokesman at the Pentagon.

Troops must have operated within 100 nautical miles -- roughly 115 miles -- from the Mexico border in Texas, New Mexico, Arizona or California, according to the Marine Corps administrative message. Those operating in San Antonio, where the mission headquarters is located, are also eligible, along with troops at sea who are within 24 nautical miles of the coast.

President Donald Trump first announced that active-duty, Reserve and National Guard forces would begin deploying to the border in April 2018. He has referred to the crisis there as an "invasion," as Central American migrants fleeing violence in their countries have overwhelmed Customs and Border Protection agents.

Under a 2018 law, Purple Heart recipients; former prisoners of war; veterans with a service-connected disability from 0 to 90 percent as documented by the Department of Veterans Affairs; and certain primary veteran caregivers will be newly eligible to shop at commissaries and exchanges. It applies to all military bases, including Coast Guard.

Medal of Honor recipients and veterans with a VA-documented service-connected disability rating of 100 percent and their authorized family members have long been authorized these privileges, under DoD policy.

As defense officials get ready for 3 million more people who will be able to shop at military stores on base, some veterans are wondering whether they’ll be able to use their new benefits.

Some veterans have contacted Military Times to say that they are eligible for the new benefit that takes effect Jan. 1, but are concerned they won’t have access to the stores. That’s because they don’t have the specific credential required ― the Veteran Health Identification Card, or VHIC, issued by the Department of Veterans Affairs.

Based on responses to Military Times queries, there are no answers yet for these veterans. Information was not immediately available about how many veterans could be affected.

The departments of Veterans Affairs, Defense and Homeland Security have been working together for months on plans for how the program will be implemented. A crucial part of that is the credential required to get onto the base and to shop at the stores, because most veterans who aren’t retired don’t have access to installations.

Defense officials are working to enable technology at the front gate to scan those veteran cards so veterans can get in to use those benefits. Commissary officials are working on adjusting their technology to enable systems to read the cards.

Some veterans have said they are eligible for the new benefits because of their disability rating, but don’t qualify for the VHIC, for various reasons. One veteran said she has tried to get answers from VA about what she can do to be able to shop, but has been unsuccessful. “I hope the VA and DoD will work together to ensure that no veterans with a service-connected disability are overlooked on this benefit,” said the veteran, who asked to remain anonymous.

“The VHIC is the only credential that DoD resale and MWR facilities will accept from veterans authorized privileges solely under the Purple Heart and Disabled Veterans Equal Access Act of 2018,” said DoD spokeswoman Jessica Maxwell. “Specific questions about who can and how to obtain a VHIC should be directed to the Department of Veterans Affairs.”

For their part, VA officials say DoD is in charge of this benefit expansion. "We are working with DoD to accommodate all eligible veterans,” said VA spokesman Randy Noller.

WASHINGTON -- Former Air Force and Navy fighter pilots are calling on the military to begin cancer screenings for aviators as young as 30 because of an increase in deaths from the disease that they suspect may be tied to radiation emitted in the cockpit.

"We are dropping like flies in our 50s from aggressive cancers," said retired Air Force Col. Eric Nelson, a former F-15E Strike Eagle weapons officer. He cited prostate and esophageal cancers, lymphoma, and glioblastomas that have struck fellow pilots he knew, commanded or flew with.

Nelson's prostate cancer was first detected at age 48, just three months after he retired from the Air Force. In his career he has more than 2,600 flying hours, including commanding the 455th Air Expeditionary Group in Bagram, Afghanistan, and as commander of six squadrons of F-15E fighter jets at the 4th Operations Group at Seymour Johnson Air Force Base in North Carolina.

Last month McClatchy reported on a new Air Force study that reviewed the risk for prostate cancers among its fighter pilots and new Veterans Health Administration data showing that the rate of reported cases of prostate cancers per year among veterans using the VA health care system across all services has risen almost 16% since fiscal year 2000.

The Air Force study also looked at cockpit exposure, finding that "pilots have greater environmental exposure to ultraviolet and ionizing radiation ... (fighter pilots) have unique intra-cockpit exposures to non-ionizing radiation."

Retired Navy Cmdr. Mike Crosby served as a radar intercept officer in F-14 fighter jets from 1984 to 1997, accumulating over 2,000 flight hours. He started Veterans Prostate Cancer Awareness Inc. in 2016 after his own prostate cancer diagnosis at age 55.

"I think there's been a lot of avoidance in addressing this issue," he said. Crosby and other pilots who contacted McClatchy said they suspect the cancers in their community may be linked to prolonged exposure in the cockpit to radiation from the radar systems on their advanced jets, or other sources such as from cockpit oxygen generation systems.