I'd bet it's not rare for ex-military to enter into monastic life. It's recorded that in 495 AD, Henan's Shaolin temple inducted a couple of disciples who had combat expertise. The disciples were probably former military personnel or mercenaries. So, similar occurrences probably date back to the foundation of Shaolin.
Do you ever think about why the monastic traditions in the west were so different to the example of the shaolin temple?