Do I have to apply for Indefinite Leave to Remain (ILR) as a stepping stone to obtaining citizenship?
Previous to the change yes, but only after discharge. From now on, under the new rules, you can apply to naturalise whilst still serving without the need to obtain ILR first. If however you wish to apply for naturalisation after discharge, the old rules will apply and you will still need to obtain ILR first. Spouses and civil partners of Service personnel will in all cases first need to obtain ILR if applying for naturalisation from within the UK.