Karachi is only 500km from Oman one of our blue zones if needed we can base a lot of aircraft there(but we better boost the airforce enough to get control over the airspace above the invasion).
It's not just the airspace over the actual zone we're using as a beachhead that's the problem. It's:
1) Air and naval elements based out of India or Bintang's territory striking GDI convoys headed to supply Karachi
all over the Indian Ocean. We need broad coverage of the sea and the ability to hunt down and destroy raiding ship forces with air power if we're to hold the raiders at bay.
2) Trying to
hit back, to keep the Indian Nod warlord off-balance, because if we're not keeping them off-balance and disrupting their own coastal activities, they have much more freedom to line up their shots and put
us on the defensive. Remember that India is basically the one major warlord territory unlikely to be threatened or weakened by Steel Vanguard. Carrier air raids against the enemy coastline can do a lot to force
them to think about how to respond to
us rather than just endlessly pelting us with bomber attacks, missile attacks, raiding boat/ship/sub attacks, and so on.
The fleet carriers are a big element of our chances of supporting Karachi, and our ability to control the seas in general. There was explicit language in the last update about this...
"While so far, the raiding activities have been warded off with naval escorts, it is only a matter of time before the Brotherhood manages to do significant damage to GDI's ability to maintain global supply networks. With the Navy still distinctly short on modern hulls, and with only a relative few currently under construction, it is likely to be the element that drags GDI's offensives to a halt."
We need to do as much as we can to forestall that drag-to-halt if we want to pull off Karachi.
We should do the battleships conversoins and a frigate yard even if we try to the invasoin with air support a else we run the risk of the convoys not being able to reach their destinations in the year post Karachi
We should be trying to do as many escort carrier and frigate yards as we can
regardless because the navy urgently needs all of those ships and it needs them yesterday.
The conversion carriers in particular are only a necessity because the Navy is so overstretched, though.