What was the standard bomb load, carried by US carrier-based divebombers, during WWII, when they went after enemy carriers?
Was it contact detonation or armor piercing, to explode below?
What did they drop on the Japanese carriers at the Battle of Midway?
The largest bomb dropped on the 4 Japanese carriers was 1,000 lb. Some exploded in the hangar deck, but I believe one exploded in the engineering spacesin one of the carriers. Some also carried a 500 lb. bomb and some carried two 100lb. bombs (one under each wing). I don’t know if either the 500 or 1,000 was considered “standard.”
From “Incredible Victory” by Walter Lord, the Japanese can see ‘objects’ falling off the American divebombers’ wings so they must be 100-pounders used on Nagumo’s carriers. But I’m sure they also had 500.
As I understand it, 1,000 pounders are for high altitude level bombing. I could be wrong.
Maximum load of a Dauntless was a 1000-pound general-purpose or armor-piercing bomb carried under the belly. If a 500-pound bomb was loaded it could also carry a 100-pound GP under each wing.
At Midway, the Enterprise group seems to have carried a mix of 500s and 1000s, probably because the ship was launching both SBD squadrons (VS-6 [“Scouting 6”] and VB-6 [“Bombing 6”]) at the same time and the first planes off didn’t have as much room for a takeoff run. The Yorktown only launched one squadron, so they all carried 1000s.
Standard practice would have been to load armor-piercing when hunting ships, but I’ve never seen a breakdown that included bomb type.
Side note: several of the Yorktown pilots, including the air group commander, lost their bombs on the way to the target because of a faulty arming switch that released the bomb instead. This was rather disconcerting to the torpedo plane pilots who were flying at low altitude more-or-less directly beneath them.
According to various Bombing Squadron Action Reports for Midway dated June 1942, SBD-2 and SBD-3 planes were equiped with one Mk. 13, 1000 lb. demolition bomb or one Mk. 12, 500 lb demolition bomb equiped with Mk. 21, nose, and Mk. 23, tail, fuses, detonating 1/100 sec. after impact. Many of the planes carrying one 500 lb also carried two 100 lb bombs under it’s wings.
Interestingly, this occurred after electric bomb release switches replaced mechanical levers. Apparently, there was a tendency for the pilot to pull up on his stick when releasing his bomb with the lever. Several pilots lost their bombs when, flying toward the Japanese fleet, they simply armed their switches.
It’s worth noting that a single well-placed, well-timed bomb could destroy an aircraft carrier. A single bomb – a 1,000-pounder – destroyed the Akagi at Midway.
Admittedly, it was dropped by one of our Best pilots. 
Hey, that’s insightful! I hadn’t connected the variation in bomb weights to the crowded flight decks until now.
I’m guessing they didn’t carry armor-piercing bombs. Those strike formations were hunting the only thing that could hurt the US Task Force: Japanese carriers. And the carriers didn’t use armored flight decks. A conventional bomb deliveried via normal dive-bomb approach would probably still punch through the deck and detonate in the hangar, for optimum effect: fueled and armed aircraft, munitions on racks instead of in magazines, fuel lines laying out… One well placed bomb would have been (and was) enough, and using demolition/HE bombs would have been better for causing wider initial damage in the hangar.
I suspect AP bombs would have punched through multiple decks and detonated someplace less likely to inflict mortal secondary damage.
American carriers had no deck armor. From my cite on Akagi above:
[QUOTE=Wikipedia]
Akagi’s waterline armored belt was reduced from 254 to 152 mm (10 to 6 in) and placed lower on the ship than originally designed. The upper part of her torpedo bulge was given 102 mm (4 in) of armor. Her deck armor was also reduced from 96 to 79 mm (3.8 to 3.1 in).[17] The modifications improved the ship’s stability by helping compensate for the increased topside weight of the double hangar deck.[9]
[/QUOTE]
Bolding mine.
True that American carriers throughout WWII didn’t have armored decks. Midway and successors did. Most Japanese carriers apparently had armored decks, although some didn’t (Shokaku, Zuikaku).
So yeah, APs would have been appropriate for those particular strikes. Very effective, nonetheless. The material I’ve read emphasized that the decks and hangars of the Japanese carriers were a mess because of both prepping the strike against the US task force and for receiving and turning around the strikes against Midway Island. The Japanese fleet was probably caught at its worst possible moment, and the torpedo bomber strike’s bad luck of drawing all the Japanese air patrol down gave the dive bombers all the clear air they needed.
Brit carriers had armoured flight decks, too. From the Wiki article on armoured flight decks:
[QUOTE=Wikipedia]
After a successful kamikaze hit, the British were able to clear the flight deck and resume flight operations in just hours, while their American counterparts often could do the same, but not always; in some cases repairs took a few days or even months. The USN liaison officer on HMS Indefatigable commented: "When a kamikaze hits a U.S. carrier it means 6 months of repair at Pearl [Harbor]. When a kamikaze hits a Limey carrier it’s just a case of “Sweepers, man your brooms.”
[/QUOTE]
Bolding Mine.
I think that was the plan all along. We sacrificed the torpedo bombers to draw the Japanese CAP down and to the East, while the dive bombers came in out of the sun from the West. We knew that the Japanese would be caught refueling and rearming so we used non-armor piercing bombs to explode on the deck and in the hanger bays.
I’m pretty persuaded it was an accident that it happened that way. Doctrine would be for all the aircraft to arrive at the same time and overwhelm the defenses.
Do you also believe in the Easter Bunny and Virgins?
Total accident. We were attempting a simultaneous strike and things got fubared right quick. Flights got lost, there was no co-ordination, and everybody just went at it on their own. That’s why nobody sank the Soryu (I think).* 
Thanks for the insult but which scenario seems more likely:
We track the Japanese fleet across the Pacific, listening to their radio chatter. We launch all of our available carriers, including the wounded Lexington in a all-or-nothing gamble. We lay these ships in ambush waiting for our chance. We locate the enemy fleet and launch all available planes and suddenly, we can’t find them. But wait! By sheer luck we blunder onto them at their most vulnerable and Oh Happy Day our planes are carrying the perfect ordinance to explode high up in the ship where the bombs and fuel were lying about.
or
We tracked the Japanese across the Pacific, listened to their radio chatter and laid the perfect ambush. Let the Japanese strike first, so we can follow their planes home and so they can foul their own decks. Then, send the torpedo bombers in from the direction that the Japanese were expecting to be attacked from followed by the divebombers from the unexpected side, out of the sun? I can’t believe that Halsey, Nimitz and the rest would gamble everything they had on a hunch.
Luckily history doesn’t care what you believe.
And it was the Yorktown. The Lexington went down in the Coral Sea.
One problem with the “it was all planned” scenario is that the Japanese fleet wasn’t where the initial dive bomber strikes* expected it to be. Both groups found empty ocean at the designated point, and the air group commanders made exactly opposite choices: Stan Ring (Hornet) figured the Japanese had already passed and turned toward Midway, taking his group out of the fight; Wade McClusky (Enterprise) concluded that the Japanese had turned away from Midway and opted to retrace their reported course, a decision which led him to a Japanese destroyer whose course led him to the fleet.
And “out of the sun” is meaningless since the Enterprise and Yorktown groups approached the Japanese from markedly different directions (anywhere from 90° to 120°, depending on whose report you read).
*From Enterprise and Hornet. The Yorktown waited to recover its scouts before launching its bombers. By that time more accurate information had come in, which allowed its planes to fly a more direct course. This actually worked out quite well in that even though they launched at different times, the Enterprise and Yorktown groups struck pretty much simultaneously. This probably had an exponentially greater shock effect than two separate attacks.
Yeah, Lex was gone by then. Also, I don’t think we tracked the Japanese Midway fleet(s) by radio chatter – we knew they were coming by MAGIC decrypts, which is sort of a different thing. And the ordnance used was the standard ship-killing bomb choice: armor-piercing. Also, according to Shattered Sword, the Japanese carrier decks were NOT littered with bombs and torpedoes. Everyone agrees the Kido Butai (Japanese term for “carrier strike force”) was in the process of landing, re-arming and re-fueling their fighters while they engaged waves of American torpedo bombers…
Well, you can’t land and launch fighters while the deck is filled with a strike package arming to take off. Not on a WWII straight-deck carrier. So even though Fuchida has been quoted as a primary source for decades, it appears that his description of the condition of the Japanese carrier decks at the moment of the attack must be false.
Also, you spelled ordnance wrong.
Don’t take my word for all the above. Read Shattered Sword: The Untold Story of the Battle of Midway and see if it changes your thinking.