I think a lot of people are misunderstanding the significance of "cluster" here. It's not just a statistical anomaly where a disproportionate number of deaths happen in a short space of time. Clusters also happen because suicide by one member of a group can influence other people in the group to do the same thing. This is also why details of how people went about it are scarce in reporting. It's also a big reason why the infamous scene from 13 Reasons Why got removed later on.

It's hard to determine what the expected rate should be. The military as a whole skews younger and more male. But people with mental health issues tend to leave or wash out eventually. So you see a disproprotionate rate of suicide among veterans. It's where the "22 veterans a day" [1] number comes from (although later research seems to indicate the real figure is now lower).

The US military is a difficult psychological environment. Arguably, this is completely unnecessary. There are many jokes about this like having to come in on the weekend because somebody wore the wrong color socks or having to show up at 3am for a 10am formation ("hurry up and wait"). Also, the US military constantly moves servicemembers around (ie PCS). Other militaries don't necessarily work that way. It's conformity taken to an extreme level.

One author (Daniella Mestyanek Young, a former Army intelligence officer herself) has written two books claiming the US military is essentially a cult.

[1]: https://www.npr.org/2015/10/01/444999996/the-number-22-is-th...