I can tell you 'from experience' that the adverse effects of smoking do not appear immediately but only after many years of continuous tobacco addiction... and legionnaires are usually young.
I used to smoke while in the army (1 pack / day) and had no problems of fitness. Now, although I quit 3 years ago, I would most probably not be able to run 8 km with full kit in less than 1h... But I'm 20 years older and 20 pounds heavier !