This year’s Chairman of the Joint Chiefs of Staff USO Holiday Tour has played at an aircraft hangar in Germany, in a maintenance facility and in an in-processing facility here in Afghanistan. The tour’s stars -- Kid Rock, Kellie Pickler, Lewis Black, Tichina Arnold, Zac Brown, Kathleen Madigan and John Bowman -- have played far more prestigious venues, but probably none as appreciative. And their usual audiences generally don’t get this warning: “In case of a rocket attack, let’s do what we always do – hit the ground and count to 100,” Army Brig. Gen. John Nicholson, deputy commanding general...