Do I need an lawyer?

What is the name of your state? VA

I have recently been made aware that the state of California is filing to reassess my child support. I get the impression that this involves going back to court?
My daughter's mother has apperently been unemployed for nearly 10 years (actuallly she does home child care but proving that sort of thing isn't easy) and is on State assisstance (Welfare/Foodstamps), insurace is provided by the military.

I read a little on the DSS web site and checked the support calculator but I'm not sure if I understand it fully.
The way I calulated it, it looked like my current wife and 3 kids would be better off if I divorced them, payed them child support and alimony and took the remainder and went to live on the ship(a dubious benefit of being in the Navy).

I currenly make around 50000 a year and pay about 400 a month CS.
Should I hire a lawyer?
Am I going to have to do this every 3 years?

oh yes!

Get a lawyer to assure you are represented properly...
however, if the order is out of CA, which I assume it is from your post, please know that BOTH parents income figure into support amounts and she, indeed, needs to be supporting the child/ren, as well.
CA is a shared income state and even if she is not working (getting a wage/check), I would insist they input income for at least minimum wage/40 hours a week. IMO
Do you have set visitation? Parenting time percentage also figures into CA support amount.

You might also try this site-
www.deltabravo.net

Best wishes