JON PARSHALL SPEAKS ABOUT THE INITIAL HIRYU LAUNCH AT 10.54 A.M.
The successive attacks by the American Navy torpedo bombers, pressed home resolutely and with appalling losses, kept the Japanese carrier flight decks occupied with activities related to recovering, rearming, refueling, and relaunching more than forty Zero fighters that were protecting the carriers. This point has been made by Jon Parshall, an internationally recognised expert on Imperial Japanese Navy operational doctrine:
"Taken together, it is apparent that spotting a twenty-one plane strike for launch would take around forty minutes total, and another five to ten minutes would be required for the launch....Thus if Nagumo was to attack the American strike force, he needed to find an unbroken forty-five minute window of opportunity on all four flight decks during which to spot and then launch his strike".
"Doctrine Matters: Why the Japanese Lost at Midway", published in the Naval War College Review 2001 (at pages 2-3 of the web version).
A close examination of the sequence of eight separate torpedo and bombing attacks between 0705 hours and 1022 hours does not suggest the existence of that "unbroken forty-five minute window of opportunity on all four flight decks".
The four surviving TBDs of VT-6 cleared the Japanese carrier force shortly after 1000. Yorktown's torpedo squadron VT-3 was sighted approaching the Japanese carriers at 1010. The attack by VT-3 was focussed on the carrier Hiryu. During this uncoordinated attack, several torpedoes were dropped between 1020 and 1030. The captain of Hiryu skilfully evaded all of the American torpedoes. The two surviving planes of VT-3 cleared the Japanese carriers and their screening warships at about 1035. Despite being the focus of torpedo attacks between 1020 and 1030, it is recorded in the Nagumo Report that Hiryu began launching its initial strike at the American carrier force at 1054. The launch was completed at 1058.
If Hiryu had to recover Zeros from the combat air patrol before it could "spot" bombers on its flight deck, the recovery operation would probably have taken at least five and more likely ten minutes. However, if Rear Admiral Yamaguchi was prepared to give top priority to launching his bombers at an American carrier, and "waved off" any returning Zeros from the combat air patrol, then he would have had about thirty minutes at most to move them from their hangars to the flight deck and prepare them for the launch which is timed by Nagumo as beginning at 1054.
Applying Jon Parshall's timings for preparation and launch of a Japanese carrier strike, it is difficult to see how the Hiryu strike could have been spotted and launched in roughly thirty minutes. It should have taken at least 45 minutes to move the eighteen Aichi Val dive-bombers from Hiryu's hangar deck to flight deck, warm up the engines, load bombs, etc, and begin the launch. This timing would have required preparations for the Hiryu launch to have begun at 1010. The timings are not without significance for the outcome of the battle because the speed of the Hiryu launch appears to have enabled the Japanese pilots to catch up with and follow Yorktown pilots back to their own carrier.
The Hiryu launch time raises important questions. Was Hiryu a special case? Did preparations for an anti-ship strike begin on Hiryu at 1010 and continue despite the carrier being under attack by VT-3?
Jon Parshall very kindly provided the author with his views on the Hiryu's launch time.
I've mulled on that question as well. Hiryu launched three fighters at 1013, and then her records show the Tomonaga strike going up at 1057 - a forty-four minute gap. However, supposing she didn't start spotting Tomonaga's birds until 1025 or so, they did the whole thing in about thirty minutes. I don't know what the answer is there - whether they began spotting a bit earlier, or whether they just really humped it after witnessing the attacks. My guess is that it may have been a mixture of both.
Bear in mind that Senshi Sosho mentions that Soryu may have brought some of her strike fighter Zeros up to the flight deck immediately before being smacked. Bear in mind, too, that since dive-bombers were typically armed on the flight deck, which could take a little longer, Yamaguchi may have been trying to get a jump on things. My sense is that CarDiv 2* was a little further along in its preparations than CarDiv 1.** Then, after the catastrophe, I think Hiryu's deck hands simply put the pedal to the metal and got her birds ready - minimal warm ups while slapping the bombs on and GO! Either way, though, they clearly were spotting in the teeth of VT-3's attack, which didn't even commence its final runs until 1030-1035.
It's interesting to note that during Tomonaga's attack, the HE (high explosive) flak suppression bombs dropped on Yorktown didn't come from the planes in the chutai that you'd expect - typically the lead shotai would have had those weapons. But they came down from planes in the middle of the batting order. That, to me, is suggestive of a very abbreviated deck spotting sequence - just grab whatever bomb is handy to hand and get it on the plane. Hiryu had to be thinking that she might be subjected to another attack like her sisters had just suffered - speed was the order of the day. Anyway, that's my take on the matter, with the evidence I've got at the moment.
* Carrier Division 2 comprised carriers Hiryu and Soryu
** Carrier Division 1 comprised carriers Akagi and Kaga
"Chutai" is a tactical formation of nine aircraft. "Shotai" is a basic tactical formation of three aircraft.