As of January 1941: "There are now in Oahu 26 3" fixed anti-air craft guns (of which something over half are grouped about Pearl Harbor), 56 mobile 3" guns, and 109 .50 caliber machine guns. " That was judged inadequate as of the report I'm quoting, so by the end of the year I'm pretty sure those numbers are much higher...to which can be added the guns and manpower of every ship in the harbor. 50 caliber AA and dedicated 3" AA batteries are much better at shooting down planes than 8mm machine guns. As mentioned, even with only the time between the first and second wave, they got enough crewed to shoot down 17% of the dive bombers of the second wave, so they can't be written off as ineffective, either.Don't underestimate them. According to my great-grandfather's diary, those things were an absolute pain in the ass to shoot down. They could survive quite a few 8mm Mauser rounds fired from ZB 26s or whatever MG his troops had. The real question is how many flak guns and AAMGs US forces can man by the time the 3rd wave shows up.