Let me toss a few more questions out there.
Why does the Fletcher-class destroyer, carrying five 5 inch/38 caliber guns, have an Attack rating of 22, a Defense rating of 14, and a Bombardment rating of 18, while a Brooklyn-class light cruiser, with fifteen 6 inch/47 caliber and eight 5 inch/25 caliber guns have an Attack rating of 16, a Defense rating of 12, and a Bombardment rating of 12? The destroyer had an approximate displacement of 2100 tons, while the cruiser had a displacement of 10,000 tons.
The B-17 has a bombardment rating of 18, and normally carried a load of 4,000 pounds. The B-29 has a bombardment rating of 18, with a higher rate of fire of 5 compared to 3. The B-29 could carry 12,000 pounds of bombs for 1600 miles, with a maximum load of 20,000 pounds. The B-36 has a bombardment rating of 18, with a rate of fire of 6. The B-36 could carry 10,000 pounds of bombs for 3600 miles, and had a maximum load of 72,000 pounds. After the war, it test dropped a 44,000 pound bomb. By the way, the medium bombers B-25 and B-26 both have a higher bombardment rating than the B-17. Their maximum load was 3,000 pounds.
The Yorktown-class, the Wasp, the Essex-class, and the Midway-class fleet carriers all can carry 9 aircraft. The Independence-class light carriers can carry 4 aircraft. The Bogue-class and the Casablanca-class escort carriers can carry 9 aircraft. The Escort Carrier air groups were smaller than the light carriers in reality. Typically they carried 21 aircraft, while the lights carried 33.
Then there are the Japanese Zeros with a range comparable or greater than that of the B-17. Some of the aircraft ranges are truly bizarre.
The Japanese I-400 class submarines were designed to carry 3 attack float planes for strikes against the U.S., and carried a single 140mm/5.5 inch deck gun. They are not given any aircraft, but do have a bombardment rating of 18. See comments above.