Hi guys I'll get straight to the point, Im currently training to join the Marines in a year when Im 18, I need to be able to run 3 miles in 21-18 min (18 preferably). I've been running miles (or pretty close to a mile) everyday for about 4 days, I can run it fine but I need to take walk breaks probably 2 or 3 times for like 30s each my overall time is about 8 or 9 mins.

What is the most efficient way to train for a 3 mile run? Is a mile a day enough to get there? I heard some things about alternate between long runs and sprints. Lastly is it possible to get from where Im at to running an 18 min 3 mile if I train hard?

Thanks in advance for replys.