We hypothesize that an anecdotally observed increase in tourniquet breakage and decrease in efficacy may be secondary to environmental exposure during military deployment. This was a study comparing efficacy and breakage of 166 Afghanistan-exposed tourniquets to 166 unexposed tourniquets. Afghanistan exposure was defined as tourniquet carriage by field staff in the operational environment for approximately 6 months. In a controlled environment in the United States, a previously exposed tourniquet was tested on one thigh of each subject, while an unexposed tourniquet was tested on the opposite thigh. We recorded tourniquet efficacy (absence of distal pedal pulse for at least 30 seconds), breakage, and the number of turns required to stop the distal pedal pulse. A Wilcoxon sign-rank test was used to test differences between exposed and unexposed tourniquets. Tourniquets exposed to the environment broke more often (14/166 versus 0/166) and had decreased efficacy (63% versus 91%; p < 0.001). Three turns were required for most tourniquets to be efficacious. Environmental exposure of military tourniquets is associated with decreased efficacy and increased breakage. In most cases, tourniquets require three turns to stop the distal lower extremity pulse.