When I ask senior military, as I did last night and last week, to construct plausible scenarios in which Britain's giant new supercarriers would be essential for the defence of the realm, these admirals and generals looks slightly embarrassed.
When pushed, they mention the possibility of two great powers (not Iran) turning into serious enemies of the UK.
I won't mention the names of those countries (though you'll guess which they are), because those same military leaders hastily add: "of course we'd be insane to even think about going to war against them; we should be building permanent enduring alliances with them; and if we did find ourselves at war with them, the carriers would probably be sunk in five minutes".
http://www.bbc.co.uk/blogs/thereporters/robertpeston/2010/10/what_a_carrier_on.html