Sorry, I doubt that. In the middle 70s it was COBOL, when COBOL'74 came out it became king of in-house programming for IBM and many other companies.

Now if you said the 60s or science based programming, I would agree with you about FORTRAN. But in-house usually means running the business, that is where COBOL rules.

Now, in-house is SAP ABAP, I think that took over at IBM in the mid to late 90s and early 00s. But IBM is moving to the next release of SAP and from what I heard from people there, ABAP is being phased out for something new that SAP came up with.