After we celebrated the Fourth of July with a family barbecue, my 18-year-old son, Sam, shipped out for Marine Corps boot camp in San Diego. The idea of having a son in the military still seems strange, but I’m starting to get used to it.

When Sam announced his decision, it seemed mystifying that my not-terribly-athletic, bookish son would decide that what he wanted most of all was to be a Marine.

My friends were shocked and offered plenty of advice — he should see a psychologist; he should consider the Navy; did I realize how underhanded the recruiters could be?

But Sam never had an easy time at school, and he wasn’t interested in college, at least straight out of high school. He wanted to be a Marine, period. Since he was a toddler, he’s been fiercely stubborn, a child who did exactly what he wanted without much interest in the approval of teachers or parents.

For years, he read up on World War II and the Vietnam War and devoured war novels and fighter plane encyclopedias, though he had little use for history classes at school. It didn’t occur to me what his hobby might lead to. We didn’t know a single person who served in any branch of the military, other than the grandfathers who fought in World War II.

In some circles, Sam’s decision might have seemed practical, even heroic. But in our liberal, antiwar sphere, his desire to enlist was met with shock — even hostility. I wasn’t really surprised at our friends’ reactions — after all, Sam’s dad and I were initially opposed. We talked to him over and over about the risks he would face, the unyielding obedience he would need to summon. We spent the last year trying to inject some reality into his somewhat idealized vision of the military, but true to form, his mind would not be changed.

As the parent of a high-schooler, I had to answer the same question at every social event or Trader Joe’s encounter: “What is your son doing about college?” That was a hard question, because though I didn’t agree with him, it was still his choice, one he felt strongly about.

Often the reaction was pity or even anger. A friend with anarchist leanings pleaded with me to get him counseling. One mother stated firmly that she felt her job as a parent was to raise her daughter so that there would be no chance she would ever join the military. A few people warned that even though he had selected a noncombat job category, the Marines might still require him to face combat. Was that supposed to make me feel better? Because it didn’t.

Once I got over my initial reticence and started talking to other parents about his choice, I found out that Sam wasn’t the only kid we knew who was interested in the military. One boy had nearly joined up but was derailed when he got a mononucleosis-like illness. A colleague’s nephew — a British citizen — was accepted into the Marines. Another friend’s son decided to become an Army medic even though he was nearly finished with college.

My son passed his high school equivalency exam last summer and signed his enlistment papers in the fall, with the understanding that he would be inducted after completing a year of community college. The decision seemed to agree with him. After years of never really getting with the program, years of endless struggles over toothbrushing and homework, he changed in the months after enlisting.

The bedroom that had been the typical teen vortex of dirty plates glued to gaming magazines was suddenly organized and vacuumed. For the first time ever, homework was getting done and chores accomplished, at least some of the time. Despite weekly karate classes, he had started the year with the typical gamer’s pudge. Now he woke early on Saturdays for physical training with the recruiter. He watched his diet, joined the Y and got the highest score in his bodybuilding class.

It seemed as though he was ready for basic training, but we were still worried about what would come after.

Sam selected aircraft information systems as his job (which, thankfully, involves an entire year of training in mellow Athens, Ga.), and he says if the Marines need him to go into combat, he’ll do what is asked of him. Of course I’m worried about Afghanistan, tanks, injuries, psychological scars — but worrying hardly seems productive.

So he’ll be an unconventional Marine — full of historical facts but short on street smarts, a noncombatant in a branch known for its combat prowess, a kid from a liberal family who’s going to really miss Los Angeles’ taco trucks when he gets to the Marine mess hall.

It wasn’t until I started chatting online with a childhood friend just a week before Sam’s ship date that I started to make peace with my son’s decision to face war. My friend’s 20-year-old son recently decided to emigrate to Israel, where he will be required to serve in the Israeli army. “College is a joke if you’re not into it,” my friend wrote. “Just an expensive waystation for bored kids.”

“It’s the first lesson in learning to release them,” he typed. “To let them do what they feel passionate about.”

And then: “Entering the military and serving your country is a lost art among us privileged Angelenos.”

I closed the little message box on the computer feeling a little less guilty that I should have done more to stop Sam and maybe even a little proud of my son for being willing to try something that is completely foreign to us privileged Angelenos.