At least in the US Navy, they've been using annual mass vaccination of sailors as an exercise. See NAVADMIN 248/19 para. 2.g. The first mention in one of these messages about an exercise is from 2012. See NAVADMIN 246/12 para. 2.f. It always struck me as odd, and being anti-vaxx since about 2014 when my daughter was born, it made me suspicious. With COVID, Warp Speed, and the article linked in 10494489, the plans are fairly clear.
All NAVADMINS for 2011 through today can be found at:
https://www.public.navy.mil/bupers-npc/reference/messages/NAVADMINS/Pages/default.aspx