Onc quick little interjection here gentlmen. The truth is that if you do some research on Running as a sport, especially training involved with road races and triathalons you will find the typical training regimen and mindset of you average athelete is completely wrong.
I remember back in high school and college sports the coach yelling at you to push it hard and fast not just in games, but practice and pre-seasonal conditioning. That is improper traiing mentality, leading to possible injury, burnout, and limiting you to a very specific result. If you train running the same distance at the same pace right from the getgo, you will be able to run ONLY the dist/pace even over a prolonged period of time with limited improvement/results.
To train properly you have to honestly assess your athletic capabilities. Are you a beginner? Intermediate? what are your short term and long term goals?
Proper training starts with a building phase(normally 1-3 months long) where workouts are long and slow staying in the aerobic zone. If your lungs and muscles are burning :icon_rage and you can't catch your breath you have reached your anaerobic threshhold. Anaerobic exercise is great for weight lifters, not so much for distance runners. and when I say distance i mean anything above a 400m dash. Anaerobic running will not improve your distance times significantly and promotes injury.
When you finish with a building workout you should feel like you worked but should also feel capable of immediately doing it again. The hardest part of building phase is not overtraining. the urge to push yourself to the edge is almost always overwhelming. More importantly vary your workout, surprise your muscles as much as possible. Vary distances, inclines. Bike and play ball on easy days.
Only increase times and your longest distance by 10% every week. You will know when your building phase is done when your running your goal distance after slowly increasing your times and suddenly...you realize its not taxing your body at all. then you can throw in a little strength training with sprints and the occasional hard run. This way you have a good base training that makes you capable of training for a much wider range of distances and your aerobic muscles will be more adaptable to whatever the marine DIs at OCS want to throw at them.
PROPER REST AND RECUPERATION ARE JUST AS IMPORTANT AS RUNNING AND LIFTING! DON'T OVERTRAIN! workout 5 days a week and don't string your two rest days together unless you have to.
Remember since physical readiness is one of the only things you can prepare for at OCS it should be a priority for every selectee. Don't expect to do an average job of getting fit and then show up expecting cupcakes and hugs

at OCS. Hell that wasn't a very quick interjection at all.

Oh well hope this helps if you take the time to read it. Good luck guys.