The origin of the submarine sandwich has only been documented back to about 1940. “Heroes” goes back into at least the 1930s. All of these names stem from “Italian sandwiches” made since the '20s-'30s. “Grinders” start showing up around 1946.
SC must be weird, because I use all of those for different things.
Gyros are usually lamb (sometimes chicken or other) on pita with cucumber-yogurt sauce, onions, and tomatoes. They’re pronounced as “hero” normally, with “gyro” coming in a close second. They are sold in Greek/Italian restaurants, and at fairgrounds.
Heroes (spelled that way) are a specific type of sammich on a long roll with multiple different types of meats. I’ve never seen a hero with less than two types of meat, usually of the ground-up persuasions. They are sold at family-owned restaurants that are older than I am, and at bars/pubs.
Subs are whatever “type” of sammich you’re going after that isn’t a hero. A chicken-tender sub, a roast-beef and swiss sub, a pepperoni-pizza sub, whatever. Usually only has one type of meat, exceptions being for club-sandwich subs, which are only (IMO) subs because of the bread used. They’re usually at cafes or sandwich shops, or at the deli/bakery counter in grocery stores
(Subs are also anything sold at Subway/Blimpie/etc due to their branding.)
Grinders are exclusively hot/melty/heated sammiches which otherwise would be either subs or heroes. They are CALLED grinders at really good ‘greasy spoon’ hole-in-the-wall eating establishments.
ETA - Hoagies are what people not from SC call subs and heroes. 
In New Orleans, it’s called a Po-Boy.
Actually, “poor boy” or " 'po boy" sandwiches seem to predate others. Definitely originated in New Orleans in the 1920s.
Po’ boy