"I'm going to have to get my skirts lengthened for that" meaning?

In the great 70s film Coming Home by genius Hal Ashby, there is a line near the beginning that I can’t really understand. Bruce Dern’s character, Capt. Robert Hyde, is sitting in the Officer’s Club with his wife (Jane Fonda) and his friend tells him, “you’ll make Major.” His wife then says: “Major Robert Hyde. I’ll have to get my skirts lengthened for that one.” Then he replies: “Start wearing girdles.”

What does this mean?

I have no idea but would guess that she’d have to start looking more fashionable, i.e. less trampy and skinnier. (Not that her skirt length at the mo is necessarily trampy but not an appropriate length for a major’s wife.)

Yip. She’s got to look more proper if she marries someone that high up the social ladder. And proper translates to an older, more conservative style, just like it does today. Short skirts and not wearing a girdle were at towards edge of fashion in those days. The last thing a proper lady would do is look like she’s trying to be in on the latest fad.

And the fact that she made a joke out of it means the couple likely saw the whole concept of having to be a proper lady to be a joke–another trend going on in that time period.

Think of it as someone saying that she’s have to start wearing dresses instead of jeans or something.