The term "piquet duty"—if what the reporter meant was that he was on watch, on sentry duty—is archaic, has been replaced by "picket duty." But the term "piquet" or "picquet" has another meaning, which, in these days of waterboarding & sensory deprivation, is not beyond the bounds of possibility."The lance-corporal was a cook at the forward base and was taking his turn on piquet duty when he was murdered by the Afghan National Army solider who had only recently arrived at the base."
To quote—forgive me for doing something I advise everybody not to do—Wikipedia:
The "picquet" (alternately spelled "piquet") was a method of torture used as military punishment in vogue in late medieval Europe.
The punishment of the picquet required placing a stake in the ground with the exposed end facing upward. The exposed end had a rounded point. The malefactor was typically a junior officer who had disobeyed orders. One thumb was suspended from a tree, while the sole or heel of the opposite bare foot was balanced atop the stake. The point of the stake was sharp enough to cause considerable discomfort, but not sharp enough to draw blood. To relieve pressure upon the tortured foot, the prisoner relegated all his weight to the thumb, all but tearing the thumb from its socket, which could only be relieved by shifting weight back onto the tortured foot.