The military Vol 6 is called the Structures repair Manual or SRM in civil parlance. Damage beyond the SRM requires a repair design done by a suitably approved design organization. Looking at the damage to that E3 I'd say its well beyond a B707 or KC135 SRM and is therefore beyond the RAF Vol 6. Boeing would easily design a repair and also provide many of the parts needed to carry it out, but its well within an M.U.'s capability to accomplish it. I don't know if any RAF M.U. has the overblow equipment to 'work' the completed repair, but that could be hired in from Boeing too. Repair design contracted out with accomplishment in-house? I reckon that makes it Cat 3.