"The ancient protocol was written with the “good chaps theory” as one of its fundamental assumptions "
Which was a proven fallacy even then.
At least one set of naval war games in the late 1970s/early 1980s ended within hours after Red team accessed Blue team's systems, downloading all their plans and intercepting orders, etc. They paralysed Blue team's deployment ability and "killed" them where they sat, in several cases by causing "self detontations" of Blue equipment without a Red team member in sight.
Blue team cried "foul" and tried to have this kind of thing banned, but it marked when the US military became interested in cyber warfare.
Academics getting onto DARPAnet brought a lot of that blind trust back, but those in the know were preaching security from the outset.