The concrete boat is an interesting idea though if what you want is more a mobile air base than an aircraft carrier. Habbakuk has at least one other advantage though - if the hull does get cracked then the stuff pouring through the breach is also the material you need to patch it. Repair under way will be somewhat more complex with a concrete hull...
isnt that what habakkuk is anyways? a mobile airbase.
the concrete version would be a much better long term investment though.
could move it to any hotspot where you would need it.