SOUTHWEST ASIA – Tucked deep within an operations center at a military base in Southwest Asia, where the United States and coalition partners coordinate operations against the Islamic State in Iraq and Syria, is a small room that keeps the U.S. and Russia from war, or at least their military forces from colliding in Syria.

Inside the small room are two workstations, a desk, and a black phone with a white label on it that says, “Russia phone.” That phone is a direct line from the U.S. military to the Russian military, to allow each side to coordinate their operations in Syria so that they do not conflict on the battlefield.

Manning the line is a team of four American troops who hold various ranks but all have one thing in common: they can speak Russian at a native or near-native level and are specially hand-picked for the assignment.

They are the ones who actually communicate with Russian forces when either side has plans that could conflict with the others. Typically, a senior leader on one side will initiate a call to inform the other side of a specific operation that needs deconfliction, sometimes calling up to a dozen times in one day.

The team will facilitate the call by putting it on speaker phone and translating what the senior leader wants to tell the Russians. Just recently, the Russians on the other end of the line added English-speaking counterparts.

The team members who spoke on the condition of anonymity said the calls are “very cordial, very professional.” One joked it was like talking to a “distant cousin” and that the conversation was “nothing too substantive.”

The number of calls per day “ebb and flow” depending on the operations. Right now, they said, deconfliction is “sporadic,” they said.

The last time things got busy was during the Russian offensives against ISIS in Mayadin in mid-October and Deir al-Zour in mid-November, they said.

The line was created after U.S. troops began air operations in Syria against the Islamic State in September 2014, and Russian air forces also began operations there in September 2015.

Despite its importance, the deconfliction line has remained a mystery for many reporters covering the ISIS war from the Pentagon.

Moscow has threatened to cut the line several times, but it is not clear whether that has ever happened. There is at least one other deconfliction line at a nearby U.S. Air Force base in Qatar where the U.S. military plans air operations over Syria.

A lot is riding on whether the team gets things right. In the past, there have been mishaps between the U.S. and the Russians. In April, the U.S. struck pro-regime forces by accident, killing 17 and sparking anger on the Russian side.

This current team manning the line arrived after that incident.

“We strive for accuracy,” one member said.