The U.S.S. Oakland is a WWII anti-aircraft cruiser.
Overall U.S. Army anti-aircraft capabilities were quite good.
Although they receive little attention, US Army anti-aircraft systems were actually quite good. Their smaller tactical needs were filled with quad-mounted 50-calibre machine guns, which were often mounted on the back of a half-track to form the Half Track M16, Anti-Aircraft. Although of even less power than Germany's 20mm systems, they were at least widely available. Their larger 90mm heavy guns would prove, as did the eighty-eight, to make an excellent anti-tank gun as well, and was widely used late in the war in this role. Finally just as the war was ending a new 120mm gun with an impressive 60,000ft altitude capability was introduced, the so-called stratosphere gun, which would continue in use after the war into the 1950s.
US anti-aircraft received little attention firing at German aircraft, due obviously to U.S. dominance of the airspace from June 6, 1944 until VE day.
The mobile quad-50's were very useful against infantry and the 90mm 'anti-aircraft' was the most reliable direct fire tank killer in the US inventory.
This is the standard loadout of the Essex Class Carrier. This was the state of the art at the end of WWII.
Aircraft (average operational complement, October 1944): 90 planes, including 38 F6F day fighters, 4 F6F night fighters, 27 SB2C scout-bombers, 18 TBM torpedo planes, 3 F6F photographic planes.
Gun Armament: Twelve 5"/38 guns in four twin and four single mountings plus a large (and variable) number of 40mm and 20mm machine guns
It's likely each fleet carrier of this type, about ten, would have carried at least 50 F6F Hellcat or Corsair day fighters into the early stages of Operation Downfall. The Corsair link has a comparison between the Hellcat, Corsair, and P-47 Thunderbolt.
The USS Little is a Fletcher Class destroyer, one of many which would have been tasked with protecting the transports, carriers, and other critical high-value naval targets. This is the standard anti-aircraft load.
5x 5"38DP - Dual Purpose
4x 1.1"AA - Anti-Aircraft
4x 20MMAA - Anti-Aircraft
"Eclipse miracle" saved the USS Boyd when it was forward deployed as a screen against kamikaze suicide attackers, deadly duty. However, it was not uncommon for experienced naval gun crews to destroy incoming fighters at ranges over a thousand yards.
On the other hand...
I claimed of the Essex Class aircraft carrier "This was the state of the art at the end of WWII."
Perhaps I was wrong about that. There were ten Essex Class fleet carriers in service for a potential Operation Downfall.
There were also a number of Ticonderoga Class fleet carriers available, and more coming all the time.
This is the most obvious difference:
Throughout the very large program to build Essex class aircraft carriers, modifications were constantly made. The number of 40mm and 20mm anti-aircraft machine guns was greatly increased, new and improved radars were added, the original hangar deck catapult installation was deleted, the ventillation system was massively revised, details of protection were altered and hundreds of other large and small changes were executed. In fact, to the skilled observer, no two ships of the class looked exactly the same.
Beginning in March 1943, one visually very significant change was authorized for ships then in the early stages of construction. This involved reshaping the bow into a rather elegant "clipper" form to provide deck space for two 40mm quadruple gun mountings, thus greatly improving forward air defences. Thirteen ships were completed to this "long-hull", or Ticonderoga, class. Four of these were finished in 1944, in time to join their Essex class near-sisters in Pacific combat operations. The rest went into commission between early 1945 and late 1946.
That makes a potential of 23 Essex and Ticonderoga Class fleet carriers - ignoring jeep carriers, anti-sub carriers, land-based planes, and other classes of fleet carriers in operation off the shores of Japan by the end of 1946.
23 fleet carriers with 60 first line fighters of the Hellcat or Corsair variety each is not unreasonable. There was plenty of land-based bombing to allow the carriers to concentrate on killing the kamikazes.
At the kickoff of Operation Downfall that number might have been closer to 'only' fifteen fleet carriers of those two classes.