Well, WhatsApp is famously used by politicians all over the world. I would guess that the military do have secure encrypted means of communications but these ar

Well, WhatsApp is famously used by politicians all over the world. I would guess that the military do have secure encrypted means of communications but these are probably to be used at actual military operation and are probably very inconvenient to use. On the other hand, it's very convenient to communicate with your social circle and professional using the same device even the same app. By military purposes they probably don't mean to message buddies to break the door during an operation, for this they will use proper military gear. However you can imagine military personel discussing military stuff on WhatsApp etc. Stuff like scheduling things, clarifying information, discussing classified stuff to form an opinion or make a decision.