In reply to bradzy_c:
It is all good advice from the guys above,
I'm in the military and have run the same mile and a half many times, the thing is I know you need to pass the fitness test on a treadmill to get in first and foremost but once you have you will never run the 1 1/5 mile on the treadmill again. It's on a course around playing pitches outside not matter what the weather.
I trained by running a mixture of 3 miles and intervals then once a week a longer run, say 45 mins-but I wasn't bothered about distance for that run. Then every two weeks I would do a best effort mile and a half on treadmill (everything else was outside.)
But also don't focus everything on running, put some weights into your workout it will help tone you and improve your running, but you have to do sit ups and press ups in the test too. And general muscular fitness will help you through your training.