324098 Easy javascript onchange popul

I am starting a military website and would like the user to be able to select various predefined details and have the following dropdown box show different contents depending on what was chosen prior. Here's an example: They are asked if they are civilian, veteran, guard, reserve, active duty. If they choose anything other than civilian the next drop down will appear and will ask enlisted or commissioned. Regardless of which they choose the next dropdown will ask: Army, Air Force, Navy, Marines, Coast Guard. Depending on which they choose the next dropdown will show bases for their particularly selected branch of service. The names of the bases can be found by going to: [login to view URL] All bases for all branches will be used. However if they choose Army then only Army bases will populate in the dropdown. Code will be written in PHP and should include value variables so in case the form is refreshed, or there is an error and needs to be redisplayed to the user, the form should show the last options chosen.