Also from my understanding it is still taught at West Point and other major military schools, though I cannot confirm that for sure (also not a veteran). That should speak to its resounding application in our modern world.
Also good to note, like all 'wisdom', it is applicable outside of the author's immediate example if you sit back and bring the context into a modern equivalency. See an example here on how to do that, specifically Section II:
The Contextual Method Of Biblical InterpretationII. Interpretative Questions
Our discussion of a historically informed and textually-focused methodology will revolve around seven interpretive questions which one must ask in the study of every Scriptural context.
1. What did the original author say? (textual criticism)
2. What did the original author mean? (exegesis)
3. What did the original author say elsewhere on the same subject? (parallel passages)
4. What do other biblical authors say on the same subject? (parallel passages)
5. How did the original hearers understand the message and respond to it? (historical application)
6. How does this truth apply to my day? (modern application)
7. How does this truth apply to my life? (personal application)]
Translated into a secular work (like The Art of War):
Additionally, one can apply this to concealed carrying or much smaller (IE 1 v 1 or even 1 v 5) conflicts rather than full scale war.II. Interpretative Questions
Our discussion of a historically informed and textually-focused methodology will revolve around seven interpretive questions which one must ask in the study of every other-cultural context.
1. What did the original author say? (textual criticism)
2. What did the original author mean? (exegesis)
3. What did the original author say elsewhere on the same subject? (parallel passages)
4. What do other authors from the same era and culture say on the same subject? (parallel passages)
5. How did the original hearers understand the message and respond to it? (historical application)
6. How does this truth apply to my day? (modern application)
7. How does this truth apply to my life? (personal application)]
Worth the read (and re-read).