First of all, don't try to go straight into the SeALs, 18 is too young for that much responsibility. If you don't make it through they will send you to the WORST job. What you should do is go into a fleet job of your choice, learn a skill, then after your first enlistment is up you can try out for the SeALs, if you don't make it they send you back to your prior fleet job, get it? Then you can try again and your fleet job skill will make you a better SeAL. As I told you on your other question, go SWiCC first, then work your way up to SeALs. The same if you decide to go into the Army, don't go right into Green Berets, work your way up, infantry, then Ranger, then Special Forces. Or Air Force go TACP then CCT. Or Marines, go infantry, Recon, MARSOC.