What led to this new usage? Are there any clues as to its origin (i.e., is there a particular journalist or political figure who introduced it)? Is it on the upswing as I suspect (are there any reputable dictionaries which attest it)?
For most of my life, I understood troop to mean a body of soldiers, as attested by Etymonline.com:
1540s, “body of soldiers,” from Middle French troupe, from Old French trope “band of people, company, troop” (13c.), probably from Frankish *throp “assembly, gathering of people” (cf. Old English ðorp, Old Norse thorp “village,” see thorp). OED derives the French word from Latin troppus “flock,” which is of unknown origin but may be from the Germanic source.¹
But in the past twenty or years or so I have noticed troop used, particularly in journalism, to mean an individual (a “trooper”). This usage seems to be on the upswing. Here are two typical examples from last year:
Taliban insurgents killed 10 Afghan troops in an ambush in western Herat province, police and government officials said Tuesday, as one U.S. troop was killed in an attack on the other side of the country.²
The Huffington Post
Among the combat wounded from all the military services are 1,572 patients with major limb amputations, including 486 wounded troops with multiple amputations. These numbers do not include those who suffered the loss of fingers or toes.³ [emphasis added]
I have not yet seen the true singular form meaning an individual attested by any dictionaries, but it is definitely in use as shown above.