Data import in MON-YY format - has to be stored as text - how can it be converted in report

Summary

I have issues with converting a text field to a date field in format MON-YY

Content

I have a file I need to manually import and it has a date value in the MON-YY format.  It's going into a custom object so I had to make that a text field since it was not actually in date format and had that - in it.  But when I get it into a report, I was trying to convert that to a date so I could sort on it.  But it's not letting me do a MON-YY format on the date in a to_date function.  What am I doing wrong?  Or is this just not possible?