If you do decide to go in, embrace it. It really can be a defining experience. I would have never been able to see as much of the world as I did if I hadn't enlisted. I definately wouldn't join the Marines though. The Navy was a really cool thing. I lived on fast attack carrier called Kearsarge. I was a Damage Controlman which means I was a firefighter/ chemical weapons specialist. We were fired upon a couple times. Those ships that were attacked in port two summers ago in Bahrain, that was us. As far as smoking while enlisted, I got away with it a couple times myself. We used the same sample bottles for testing AFFF as the Master-at-arms used for whiz quiz and many of my friends were simply non-smokers so it worked out. Also there is the 30 day leave. You'll be in top shape so your system will process THC pretty quickly. Good luck whatever you decide, but I wouldn't do it.