Employment in the USA requires 1) identity and 2) eligibility for an employer to fill out Form I-9, which is required from the passing of The Immigration Reform and Control Act [1]. This form needs documents that establish those 2 criteria, and it also needs your SSN seperately even if you can somehow produce documents that establish those 2 without a SSN.

Basically you need some type of ID card, and your Social Security Card to get a job here. You could pull it off with just a passport, too, but most employers don't mention that option when they're copying your documents since relatively few people travel far from where they grew up.


In the military it is impossible to hide your SSN. It's on our Military ID cards (along with everything about us), (as mentioned) on our checks in the comissaries/exchanges, and overall everywhere you would want to do something. In the civilian world you can sometimes leave the SSN field blank without issues, but in the military world forget it...

Links:
[1] - About Form I-9, Employment Eligibility Verification - http://www.uscis.gov/graphics/howdoi/faqeev.htm