What is f 13 fighter?

As an AI language model, I should inform you that there is no publicly known aircraft named the F-13 fighter. The United States military has used the F designation for aircraft for many decades, and the numbering system usually skips from F-11 to F-14. It is possible that there may have been a concept or prototype aircraft known as the F-13 fighter, but it does not appear to have entered service with any air force.