The loss of six American airmen, including four federal agents, in Afghanistan provides proof that combat is not over as far as the Taliban are concerned.

Since the tragic attack on US forces in Afghanistan on December 21, there have been abundant news reports about the six US airmen who perished and the two individuals who were injured in a cowardly Taliban suicide bombing of a security patrol. But few Americans understand who they were, the dangerous nature of their jobs, and the fact our soldiers, sailors, and airmen are still being killed in a war zone where US forces have supposedly ended combat operations.

Of the six individuals killed in action, four of them—Major Adrianna Vorderbruggen, Staff Sergeant Michael Cinco (from Mercedes, TX), Staff Sergeant Peter Taub, and Staff Sergeant Chester McBride—were more than just Air Force personnel; they were federal agents with a little known investigative service called the Air Force Office of Special Investigations, generally called OSI in military circles. This attack, and the circumstances under which it happened, has hit me very hard; I used to be one of them.

OSI is the Air Force’s equivalent of the FBI. Its agents are responsible for investigating mostly felony-level crimes committed by or against Air Force personnel around the world. The agency is also charged with engaging in counterintelligence and counterespionage investigations, protective service operations (like the Secret Service), and force protection (a.k.a. counterterrorism) operations. This last mission comprises the bulk of what OSI agents do in deployed theaters like Afghanistan and Iraq.

And therein lies the tragedy and true heroism embedded in how these agents—and their two Air Force Security Forces partners, Technical Sergeant Joseph Lemm and Staff Sergeant Louis Bonacasa—perished on December 21. The “Chair Force” is much maligned by other services for working in cushy air conditioned offices, enjoying lush golf courses and visitors’ quarters on base, and flying drones from the comfort and safety of a warehouse.

However, OSI agents in the field are often some of the few individuals authorized to go “outside the wire” in places like Afghanistan. The six airmen killed by the Taliban were on a very common security foot patrol, looking for signs of danger like a potential mortar or rocket launch site. Agents go through an untold number of villages and towns with translators, getting to know the local population and cultivating sources who can inform them of potential dangers to US bases nearby. They are skillfully trained, and many of those killed had at least one combat tour under their belts already. They also work very closely with Security Forces personnel, who are responsible for air base ground defense.

I was privileged enough to serve on active duty in the Air Force as a Special Agent for eight years before I was medically retired in 2005. I did not personally know any of the deceased agents, but that doesn’t diminish the heartache. AFOSI is a very small and tight-knit family, and I have been in contact with many active, former, and retired agents who either worked with or had come across Special Agents Vorderbruggen, Cinco, Taub, and McBride. There is no good time for such a tragedy, but the loss right before Christmas comes at a brutal time for these airmen’s families and those of us who wear or have worn the badge.

Afghanistan is not over. We are still fighting there, no matter what President Obama says. Despite the official end of combat operations in 2014, there are currently around 9,800 US military personnel deployed to various parts of Afghanistan technically serving in an “advise and assist” role. Politically, this plays out well on televisions and the Internet, leading Americans into a false sense of security and hope that all our military personnel are out of harm’s way. They are not. This was the deadliest attack on US military forces in Afghanistan since 2013, and the biggest single blow to AFOSI since three agents were killed by a roadside bomb in Iraq in 2007.

The remains of these six heroes will be arriving today at Dover Air Force Base in Delaware, where they will be honored by friends, family, and colleagues. My heart is shattered not only for the loss of their families, but because I know there may be more tragedies like this one. Afghanistan is not over. And our support for silent protectors like these brave heroes must never be over.

Sylvia Longmire is a service-disabled veteran, border security expert, and Contributing Editor for Breitbart Texas. You can read more about cross-border issues in her latest book, Border Insecurity: Why Big Money, Fences, and Drones Aren’t Making Us Safer.