Regarding some of the stuff about how far people can/can't march.
I've never been in the army or military so I can't speak of that, I'm just a regular guy.
When I did the Welsh3000s it was ~30 miles of mountainous terrain with and awful lot of ascent and descent (some estimates range around 14000 ascent and about 14,000 descent) I carried a daypack that probably weighed in at around ~10kg so what 22lbs? That was hard and the clock was running for 21 hours total (including breaks).
In preparation for that I probably never walked more than 8 miles in one go and far more likely was it was closer to 3-5 miles. I was going to give myself a month to train/prep for it but that ended up to being 2 weeks due to illness.
With a load approaching 20kg (44lbs) in Tasmania the longest day I did on the trail was only 12 miles I think. That day had quite a bit of ascent but couldn't put a number on it. Left the trailbook in Australia
I reckon people can walk further than they think, a lot further, humans are well designed for walking long distances. It's a matter of mind over matter. BUT adding heavy packs does have a big impact that takes time to adjust to, there is a lot of value in being ultralight.
In his great book Natural Born Heroes McDougall talks about JFK's 50 miler challenge that came from Teddy Roosevelt's order that US marines had to be able to do 50 miles in under 72 hours.
Bobby Kennedy did it in 18 hours and then the public got involved, it sparked a surge of interest and
Speed records tumbled: Bobby Kennedy was beaten by a high school girl in California, who was edged out by a 58 year old postman in New Jersey, who was bested by a Marine who smoked it home in under 10 hours
McDougall says the challenges died out after Kennedy was killed but there is still one today called the JFK 50.