During the early seasons of “Emergency,” John Gage and Roy DeSoto looked very neat and professional as new firemen/paramedics. They both wore their hair in a short and, no doubt, Los Angeles Fire Department regulation-approved style. Even the other men, like the loquacious Chet Kelly, wore their hair in a short and neat style.

However, after the first few seasons of the show, John, Roy and Chet started to look increasingly scruffy, what with much longer hair and that Frito-Bandito mustache that Chet started sporting. In fact, wasn’t there an episode, where a visiting fire captain scolded Chet, telling him to get a hair cut and trim his thick mustache?

At the same time that “Emergency” was aired on NBC, the much-underated “Ellery Queen” detective series was also on NBC. Kevin Tighe guest-starred as a NYC police detective on an episode of the show. To say that Kevin looked out of place with his long, 1970s hair style in a series that they took place in 1947, is an understatement. Kevin looked as out of place with that longer hair style of his on “Ellery Queen,” as Loretta Swit did with her long and flowing 1970s, Farah Fawcett coiffure as the Korean War, 1952, by the book, US Army Major Margaret Houlihan on “M*A*S*H.”

Talk about hair style anachronisms! It’s just like the actors on “Happy Days” wearing long, 1970s hair styles on a show that was set in the mid-1950s. Then again, “Happy Days” truly jumped-the-shark after season two, when the late Garry Marshall changed the show’s format from filming on a closed set to filming in front of a live, studio audience, full of screaming, pimply-faced, prepubescent teenagers. But, that’s a discussion for another thread.

Men’s hairstyles changed from the earlier to mid 70s, becoming longer while facial hair got popular as well. The actors were obviously following the trend. However in real life , there most likely was a dress code that firemen had to follow.

I also noticed the hairstyles on Happy Days and on MASH became like you said.

Talk about hair style anachronisms! It’s just like the actors on “Happy Days” wearing long, 1970s hair styles on a show that was set in the mid-1950s. Then again, “Happy Days” truly jumped-the-shark after season two, when the late Garry Marshall changed the show’s format from filming on a closed set to filming in front of a live, studio audience, full of screaming, pimply-faced, prepubescent teenagers. But, that’s a discussion for another thread.
The Waltons was way worse.
1970's hair and jeans in the 1940s.