Two former heads of the Royal Navy had warned a decision to withdraw Harrier jets before the arrival of new Joint Strike Fighter F35s in 2018 would leave Britain unable to fight another Falklands War.
Asked if there would be a gap before the arrival of the F35s, Dr Fox said: "Yes, there could be a gap, but what is the gap in?
"Do we have a gap in our ability to project air power? The answer is no.
"The point is does Britain have the ability to use air power where we require it in defence of our national interests, wherever they are? At the moment, the answer is yes. Can I guarantee that we will be able to do that in 20-30 years? The answer is no.
"Therefore, we require carrier strike."
Dr Fox also acknowledged armed forces personnel numbers
would "inevitably... fall a bit" as a result of the settlement, which is expected to require cuts of 7-8 per cent instead of the 10 to 20 per cent originally feared.
But he declined to discuss reports the forces could lose as many as 20,000 personnel.
Announcements on precise figures will be made in tomorrow's Strategic Defence and Security Review in the wake of the National Security Strategy.