ISS has gone!
I believe the way it works these days is that a JO has to complete JOCC1 (Junior Officer Command Course) followed by JOCC2 - both held residential at Shrivenham. Then, as a Sqn Ldr, the ICSC (Intermediate Command and Staff Course), followed by A(dvanced)CSC (year long and encompassing an MA in Military Studies) - residential at Shrivenham. Most ground branches do ACSC as Wg Cdrs whereas aircrew tend to complete the course as Sqn Ldrs gaining promotion at the end of the course. Higher Command and Staff Course (HCSC) follows for those destined for very high rank - residential at Shrivenham.
The RAF also now runs 'through-life' air power doctrine training for all ranks which, for officers, commences at Initial Officer Training with the Basic Air Warfare Course (BAWC) and, for all those selected for promotion to Wg Cdr, the Higher Air Warfare Course whether they have completed ACSC or not! These 2 courses are 'trigger points' a) for commissioning and b) for promotion to Wg Cdr.
Information accurate to 2007 when I retired but updated by a daughter now serving.
Hopefully that helps.
Foldie
