My son is a Marine, deployed right now. He tested well on the ASVAB, and contracted for a career FIELD... not a specific job. Once out of boot camp and MCT, he began his A school. Guys in the same career field were weeded out as they reached their maximum potential in training... to jobs all within the range of jobs for that Career Field. Those that continued to do well got the more difficult jobs. My son is in Aviation Electronics. That Career Field covers everything from guys that change lightbulbs to the guys that do electronics maintenance on airplanes and helicopters. All within the Aviation Electronics/Maintenance career field. You will be deployed... if it's to a combat zone, you'll still be in a non-infantry MOS.
By the time they train you to do one of the technical jobs, meaning, computers, electronics, any specialty like that, they've got a lot invested in your schooling and won't just stick you in an infantry MOS.
By the way, there are some ruthless recruiters out there, but our experience with my son's recruiter was great. He never lied to us. We invited him to our "welcome home" party when my son came home on boot leave.
Just don't sign an "open" contract... that's a euphimism for "Infantry"!!!
Marine Corps Mom.