A squadron of sub-sonic aircraft with the ability to intercept an airliner
Speaking as someone who controlled QRA for nearly 25 years, I assure that that by the time you add up detection, identification, decision making, scrambling and then climbing to above 30K to intercept, identify and, possibly, engage - you definitely need to be able to go supersonic.
Which is why you keep reading those reports of sonic booms over the UK as the RAF does it.....