The US military is not a representative sample of people; it's a bunch of people with better health and fitness than the general population. And the military is an institution that will reject people from joining based on a lot of the health conditions that make COVID-19 more dangerous to them.

It's useful data, to be sure, but it also highlights that the disease can be really dangerous for people outside certain groups.

> The best way to reach herd immunity is to have lots of immune people around you.

It's not at all clear yet that recovering from COVID-19 confers any lasting immunity.