While researching some information on FORTAN, I happened to com across NASTRAN (NASA STRucture ANalysis) - a program that was originally developed back in the late 1960s by Stephen Burns of the Universit of Rochester. The Wikipedia article mentions that it contains over 1M lines of FORTRAN code.
The NASTRAN program is used to perform finite element analysis (FEM)
Additional related topics to research:
I recently decided to add FORTRAN to a collection of Lab exercises I'm assembling on github.com
I took a FORTAN class in college - but haven't touched it since then. My Lab.Fortran project will be a workspace for experimenting with some FORTAN mathematical libraries.