The use of “troop” for “trooper” by the media
Solution 1:
OED has a citation:
troop, n.
2 pl.
a. Armed forces collectively. Also fig.
1598 R. Barret Theorike & Pract. Mod. Warres v.136 : Fraunce, and Flanders, too full of his pencionary troops.
So its use as a plural is long attested. However there is also
Draft Additions 1993
Chiefly in sing. [Irreg. < the collect. plural: in some cases perhaps abbrev. of Trooper n.,] A member of a troop of soldiers (or other servicemen); a soldier, a trooper. colloq. (chiefly Mil.)
and that is attested in quotation marks in 1832, and without in 1947.