Who exactly?

1.5% of the population, according to Kinsey. A bit less, according to newer research, but still not an insignificant number.

The era of free love is rather recent, and quite localized. Until not that long ago, and still today in many countries, people who are single or widows - particularly women - often live without sex for many years.

I thought it was more. I suspect a lot of married couples don't have sexual relationships anymore. I also see a lot of single persons that have a hard time (or don't even try) to find someone and so on...

Oh, I think these were just people who were sexless by choice (so, OK with it); there's probably many more who want to have sex but don't.

Asexual people

Sure, but presuming the deployed personnel are not Asexual, the problem still stands.

What problem? Non-asexual people can simply decide not to have sex, just like people decide to not eat sugar or meat.

It's not that simple, since sex is an instinct. It's hard-wired in our brains, not lile sugar or meat that are luxuries. But definitely possible with a ton of self-control.

That might be true for the average person, but since they only need a few candidates, it'd be pretty easy to select people with little or no sex drive. They are not very rare.

I don't believe truly asexual people exist the same way gay people do

I think they have depression, body issues, anxiety, etc but they don't have a true lack of sexual orientation