divorce/legal separation procedures under WA state law for military spouse on active duty

Of course you can, but you must notify the court that he is on active duty, because he probably will not be able to respond to anything you serve on him (serving him is also a difficulty), unless he gets an attorney himself. As I do not practice in your state, you need to be certain your know the laws of your county, and you should seek legal advice in your area, or visit your local court and talk to one of the family law information people there. Good luck to you!