The question...

[jmm99]

as an amateur (in the original sense of that word) in Marine history (US and CFM-Canada), I'd suggest that the two Marine kids - more likely grandkids to me - can do what they are doing because Marines are both general purpose and special operations oriented creatures[*].

They also have had combined arms for so long that they think it's a genetic feature. And can mix and match, shrink and grow, with reckless abandon (MAGTFs).

The GPF and SOF discussion(s) [re: GPF and SOF dividing lines, assuming that both of them are monoliths, which they seem not] is perceived by this detached and armchair observer to be primarily an Army thing. Although DoD Dir 3000.05, if executed fully, would affect all the services.

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[*] marsouins - sea hogs, the marine mammal with the most brains, even though no one but themselves understand their language and habits.

PS: like the photo with kids on your personal page.