Re: UK Crayon Departments are just as bad
"S5 is the Dutch military designation for failure to pass the intelligence test"
No, that would be I5. I for Intelligence.
S means (emotional) Stability.
And since long before I entered the military in the early 90s, S5 had such a stigma that it was never awarded, making S4 the de facto "maximum" score (range 1 to 5, lower is better).