I’ll respond to the part about undercovers transporting weapons and/or explosives. It’s easier to stay undercover flying commercial so a team may assemble in a location by taking separate flights and take their equipment with them. That way none of them are spotted in a known military or agency location. Or it may be a place where they can’t easily take military transport or some highly covert mission where they’d all be disavowed if they were caught. The book Rogue Warrior talks about it a little bit. If I remember correctly, everyone in Seal Team 6 had to sneak a weapon onto a commercial flight as part of training.