In August 1969 I enlisted in the Air Force, arriving at Lackland AFB in San Antonio the Monday before Thanksgiving. Air Force basic training was only six weeks, and because of the holidays we had shortened training, firing the M-16 and running the obstacle course only once instead of twice.
One day in late December it was our turn to do the obstacle course. It was quite cold that morning. When we were about 2/3 the way there, we met a Flight marching the other way. Their TI asked where we were headed and upon hearing 'the obstacle course' he said to turn around as the course was closed, as it was frozen.
And that is the reason I never ran the obstacle course.