We were always told a story about Curtis E. LeMay (blessed father of Strategic Air Command) and he would walk around the jets while they were being refueled on the ground. Poor airman/sergeant comes up to him "Sorry General, but you can't smoke this close to the refueling operations...
The B-52 still has ash trays... oddly, it's right near the oxygen regulator. We still have the checklist step... "No smoking, crew".
In the picture (yes, that's me, once upon a time) the circle is the ash tray, the square is the Oxygen Regulator control.