Tried Porting to a Cray Once
It was in the mid 80s, and the Cray salesman thought he could sell a machine to a certain 3-letter agency if only it had an implementation of the APL language. We had an APL system written in C, there was a C compiler that more or less worked, so Cray set us up with their porting center.
Once the code was running we eagerly fired up our benchmark suite, only to discover that the Cray ran them slower than a Sun workstation. The Cray salesman was crushed. Apparently the machine was really designed to run Fortran, and really only got going if you used the vector instructions. The cost of adapting our technology to fit the machine was much larger than we'd ever recoup in software licenses, so that was the end of that.
No intent to knock Cray here, only to reflect that to get value out of a "supercomputer" you really have to understand what that architecture actually is and what must be done to exploit it..