Back in 1832, the OED and M. Quinion report, 'troop' could be used singularly: "As the wounded 'troop' was not much hurt, a sort of truce was proclaimed". But John McWhorter ignored this when objecting to what he felt was a 'misuse' of "troop" -- on National Public Radio: McWhorter said: "Calling 20,000 soldiers '20,000 troops' depersonalizes the soldiers as individuals, and makes a massive number of living, breathing individuals sound like some kind of mass or substance, like water or Jell-O, or some kind of freight." McWhorter noted in particular that "this usage of troops is only possible in the plural. One cannot refer to a single soldier as a troop." ---- But one CAN, as per 1832 OED quote above. McWhorter, ignoring that, adds: "This means that mothers do not kiss their troop goodbye as he takes off for Anbar Province. One will never encounter a troop learning to use her prosthetic leg." As Quinion notes, though, it will possibly be some while, if ever, "before a member of the armed forces describes himself or herself as a troop, not least because mutual pride and loyalties within a service mean that specific terms such as "soldier" will continue to take precedence. Plus, in French, they speak of a "troup" of actors, which is still a different (French) usage. Speranza---Bordighera