You think you will make the weight?

Hi John, First, thanks for the great programming.  I've been using it for the last six months, and really couldn't be happier. However, I'm training for the Marine Corp's Officer Candidate School.  Part of its requirements is a three-mile run in 18:00 for maximum points.  I recently ran a 5k with less than satisfactory results.  I wonder what you would recommend to improve my endurance for these long runs, besides things like intervals, [...]