From: Hendaye, France
I just checked with the CV6.org site and they have the original AARs from two pilots who attacked an IJN sub on 12/10/41...I think I read that post-war it was determined they both attacked the same sub which was sunk (I-70 I think). Both claimed to have hit the water with their 1000 lb bombs within 50+/- ft of the sub.
One pilot says he was patrolling at 300 ft and dropped his bomb from about 800 ft (apparently level bombing).
The other claims to have tried a glide bombing attack which turned into a dive bombing attack due to high local winds(implies higher altitude but doesn't say how high - pilot claims the sub was moving about 16 kts though).
The following is an excerpt of her I-70 TROM:
"9 December 1941:
4 miles SW of Diamond Head, Oahu, Hawaii. At 0130 Cdr Sano reports an American carrier (USS ENTERPRISE (CV-6) arriving at Pearl Harbor. This is the last signal received from I-70.
10 December 1941:
I-6 reports sighting a LEXINGTON-class aircraft carrier and two cruisers heading NE. Vice Admiral Shimizu in KATORI at Kwajalein orders SubRon 1 and other boats to pursue and sink the carrier.
121 miles NE of Cape Halava, Molokai, Hawaiian Islands. After 0600 in the morning, Ens Perry L. Teaff's Douglas SBD-2 "Dauntless" dive-bomber of VS-6 from USS ENTERPRISE (CV-6) attacks I-70 on the surface and scores a near-miss with a 1,000-lb bomb that damages the submarine, preventing her submerging.
In the afternoon, another SBD of VS-6 flown by Lt (jg) Clarence E. Dickinson Jr. sights a surfaced submarine in the same area. Dickinson climbs to 5,000 ft for a diving attack. His plane is sighted from the submarine, which commences a slow turn to starboard, opening fire from her 13-mm machine guns. 
The bomb dropped from the "Dauntless" lands right beside the submarine, amidships. Its explosion throws several gunners over board. I-70 stops and starts to settle on the even keel, disappearing underwater about 45 seconds after the explosion at 23-45N, 155-35W.
When Dickinson returns to the scene of the sinking, he sights four IJN sailors flailing in the water. A bubble of oil and foamy water appears on the surface, followed by two more bubbles, containing oil and debris.
I-70 is the first Japanese combatant ship sunk by United States aircraft during World War II and the first fleet submarine lost in the Pacific War.
Sixth Fleet's headquarters tries to contact I-70, even after the other subs of her division return to Kwajalein. The effort is unsuccessful. I-70 is presumed lost with all 93 hands off Hawaii. "
"If I go away to sea, I shall return a corpse awash, if duty calls me to the mountain, a verdant will be my pall, thus for the sake of the Emperor, I will not die peacefully at home...."