A WSO is the equivalent of an Observer in the RN, if you have done any research on that. Take care with the ridiculously unecessary confusing language the RAF now uses, WSO's are officers (Navigators), WSOps are Senior NCOs doing Loadmaster, Linguist and Air Electronics jobs. Some WSOps get commissioned and do thier same jobs in an executive capacity, dealing with policy etc, but this is rare and at least 15 years down the road at this stage!
The Officer branch is declining, as new aircraft with blackbox technology such as integrated GPS come online. Current types using Navs are VC10, Hercs, Sentry, Nimrod (both types), GR4, F3 - check their out of service dates and take off 5 years (they won't train up ab initio Navs at the very end of the fleet life) to find out how much longer they will need Navs.