From the amount of military personnel I've met, worked with and been related to, they're the best at producing invisible ink... only a small percentage of them are not Onanists.

(bearing in mind that my sister served 8yrs as a QARANC, her husband did 20yrs as RAMC, my father did nearly 30yrs in the REME, I worked in a Military Museum for 2 years and lived in Aldershot, albeit briefly).

LTS