Custom sort for reports

[geospatial]

Ive googled this a bit, but not sure if I am putting in the right search criteria.
I have a table that has the following columns. Last Name, First Name, Rank/Grade
When I do a report I want it to sort by Rank/Grade and then Last Name. The last name part is easy, but I do not know how to set it to do by ranks, since I dont want it alphabetically. It is military ranks so COL, LTC, Maj, CPT, so on.

I am using Access 2013

 

[footoo]

Add a column and assign a number according to the Rank/Grade, then sort by that column.