Consequences for Japan plans if Britain hits Kido Butai at Ceylon?

[Admiral Beez]

Blenheims attack the Japanese carriers - 8 April 1942
Around 10:25, nine unescorted Blenheims from 11 Squadron RAF attacked Nagumo's force. They were not detected inbound by the combat air patrol (CAP). Hiryū spotted the aircraft but failed to relay a warning to the other ships. As a result, the attack achieved total surprise. The bombers unloaded at 11,000 feet (3,353 m) on Akagi; the bombs fell close to the target with no hits. Four bombers were shot down over the carriers by CAP A6M2 Zeroes, and another by Japanese aircraft returning from the strike on Hermes. In return, a Zero was shot down near the carriers and another in the returning strike. This was the first time a Japanese carrier force had faced a concerted air attack.

Let's give the RAF some luck this day, with Akagi being hit by two or three 500 lb. bombs, setting the aircraft in the hangar on fire. That's but one carrier damaged, but do the Japanese gain any insight on better CAP as they prepare for Coral Sea? And how does Akagi get home?

 

[SaparotRob]

It might serve as an impetus to get the radios to work.

 

[Thumpalumpacus]

Blenheims attack the Japanese carriers - 8 April 1942
Around 10:25, nine unescorted Blenheims from 11 Squadron RAF attacked Nagumo's force. They were not detected inbound by the combat air patrol (CAP). Hiryū spotted the aircraft but failed to relay a warning to the other ships. As a result, the attack achieved total surprise. The bombers unloaded at 11,000 feet (3,353 m) on Akagi; the bombs fell close to the target with no hits. Four bombers were shot down over the carriers by CAP A6M2 Zeroes, and another by Japanese aircraft returning from the strike on Hermes. In return, a Zero was shot down near the carriers and another in the returning strike. This was the first time a Japanese carrier force had faced a concerted air attack.

Let's give the RAF some luck this day, with Akagi being hit by two or three 500 lb. bombs, setting the aircraft in the hangar on fire. That's but one carrier damaged, but do the Japanese gain any insight on better CAP as they prepare for Coral Sea? And how does Akagi get home?

I doubt it. They got caught with their pants down and made little if any changes OTL. I don't see the bombs actually hitting changing their doctrine much. Their search failures weren't corrected either.

 

[RCAFson]

Blenheims attack the Japanese carriers - 8 April 1942
Around 10:25, nine unescorted Blenheims from 11 Squadron RAF attacked Nagumo's force. They were not detected inbound by the combat air patrol (CAP). Hiryū spotted the aircraft but failed to relay a warning to the other ships. As a result, the attack achieved total surprise. The bombers unloaded at 11,000 feet (3,353 m) on Akagi; the bombs fell close to the target with no hits. Four bombers were shot down over the carriers by CAP A6M2 Zeroes, and another by Japanese aircraft returning from the strike on Hermes. In return, a Zero was shot down near the carriers and another in the returning strike. This was the first time a Japanese carrier force had faced a concerted air attack.

Let's give the RAF some luck this day, with Akagi being hit by two or three 500 lb. bombs, setting the aircraft in the hangar on fire. That's but one carrier damaged, but do the Japanese gain any insight on better CAP as they prepare for Coral Sea? And how does Akagi get home?

Somerville's carriers actually had a pretty good shot at sinking/crippling Hiryu and Soryu (Cardiv 2) on the late afternoon, evening of 5 April 1942. Cardiv 2 became detached from the main body of the KB and had Somerville flown off a strike towards their last reported position, then ~40 Albacores would have encountered Cardiv 2 just after sunset.

 

[Admiral Beez]

I doubt it. They got caught with their pants down and made little if any changes OTL.

I'd like to think that Nagumo would be replaced, but the IJN kept him in charge of the surviving CVs even after Midway.

Somerville's carriers actually had a pretty good shot at sinking/crippling Hiryu and Soryu

If Hiryu and Soryu are destroyed on April 5th I don't expect Akagi would be hit by the Blenheims on April 9th, but imagine three IJN CVs sunk. That makes Coral Sea a different campaign for the IJN.

 

[Thumpalumpacus]

If Hiryu and Soryu are destroyed on April 5th I don't expect Akagi would be hit by the Blenheims on April 9th, but imagine three IJN CVs sunk. That makes Coral Sea a different campaign for the IJN.

In those circumstances I don't think Coral Sea happens in 1942.

 

[EwenS]

The Japanese were not stupid. Like Britain and the US they were perfectly capable of learning from their experiences in their early War operations and did so. But there was a time factor, which, given the tempo of their carrier operations meant that lessons could not always be implemented as quickly as they might have liked. Operation C to Midway was two months with Coral Sea sandwiched in between. But the changes they made did not go far enough.

Reconnaissance. Pre-war Japanese doctrine left it largely in the hands of floatplanes on the cruisers and Battleships. But the weaknesses being shown up in early operations like Operation C in the IO were very quickly being acted on. In early 1942 some pre-production D4Y1 dive bombers were modified as D4Y1-C recce aircraft with 2 being on Sōryū at Midway but not used. And at Midway they did use a couple of Kate TB to augment the floatplanes, but it still left gaps in the coverage. Unfortunately the mistakes were repeated in that battle.

But spring 1942 also saw the issue of a requirement for a new recce aircraft which led to the Nakajima C6N Saiun (Myrt) for Operation from the new generation of carriers. But it was 1944 before it became operational and then from shore bases and by then the Japanese carrier fleet was an ever diminishing asset.

Japanese Carrier operations were biased towards offence rather than defence. Right to the end the objective was to use the greater range of their strike aircraft to hit the USN first. But the lack of emphasis on defence was, at least in part due to their lack of radar, and then having got it, how to use it defensively to greatest effect. In 1942 they were about where the RN and USN had been in 1938, before radar and decent voice radio (and VHF radio) became available to them.

When it came to CAP, immediately following Midway the Japanese sought to regroup their carrier forces. Instead of 2 carrier divisions they were to be 3 carrier divisions. So Shōkaku & Zuikaku were joined by Zuiho for Santa Cruz in Oct 1942 with the latter being responsible for fleet air defence. And the number of fighters carried was increased. The objective of this was to increase the mass of air power in the carrier group and the number of fighters available for task force protection (like the USN was able to do from mid 1943). But it was 1944 before this restructuring could really be put to the test.

The Japanese got their first ship borne radar onto the Battleship Hyuga in time for Midway and expanded from there. But they failed to integrate it with their plotting facilities, even though the latter were better than other navies. And they failed to attempt radar directed shipboard fighter direction (this was done ashore late in the war). Nor did they develop an effective form of IFF.

Despite all that they were radar savvy when it came to the offence. They developed the equivalent of ASV. Allied radar characteristics were catalogued and they exploited weaknesses in those radars. And although not so advanced as the Allies, they did use countermeasures such as Window/chaff.

Friedman "Fighters over the Fleet - Naval Air Defence from Biplanes to the Cold War" is a good read on how each of the powers developed their air defences.

 

[Admiral Beez]

In those circumstances I don't think Coral Sea happens in 1942.

Meaning USS Lexington and Yorktown remain intact into June 1942. Also, with the IJN down on CVs, Sommerville's armoured fleet carriers HMS Formidable and Indomitable (does Hermes survive?) can now present an increased threat to Japan's flank. I'd love to see Sommerville meet with Nimitz and/or Fletcher in Australia or elsewhere to fight as one.

If Hermes does survive she's of little use in the PTO and should remain at Ceylon for a few months to watch how things develop, and then go the MTO to replace HMS Eagle (sunk in August 1942) or home waters for convoy work.

 

[RCAFson]

Meaning USS Lexington and Yorktown remain intact into June 1942. Also, with the IJN down on CVs, Sommerville's armoured fleet carriers HMS Formidable and Indomitable (does Hermes survive?) can now present an increased threat to Japan's flank. I'd love to see Sommerville meet with Nimitz and/or Fletcher in Australia or elsewhere to fight as one.

If Hermes does survive she's of little use in the PTO and should go the MTO or home waters for convoy work.

The RN still needs to undertake IRONCLAD and escort convoys through to Malta, so no longer term deployment of RN carriers in the IO.

 

[Admiral Beez]

The RN still needs to undertake IRONCLAD and escort convoys through to Malta, so no longer term deployment of RN carriers in the IO.

Good point. And the RN can keep possession of HMS Victorious (USS Robin) for a stronger ATO and MTO presence.

It can't be fun sitting at IJN HQ in May 1942 having just lost two or three fleet carriers and the USN/RN having lost none (to the IJN), with three Essex class, six Independence class and two Implacable class CVs under construction, and a flood of Essex, more Independence and Colossus CVs about to be ordered or begun.

 

[EwenS]

The RN, having sent 3 modern carriers to the IO by the end of April 1942, they were then gradually withdrawn after Operation Ironclad.

Indomitable - engine repairs at Mombasa until mid-July then off to rendezvous with other carriers off Gibraltar ahead of Operation Pedestal, when she suffered enough damage to send her home for repairs.

Formidable - 30 Aug 1942 left Colombo for home and a short refit before working up for Operation Torch before spending most of 1943 in the Med.

Illustrious - 13 Jan 1943 left Mombasa for refit in Britain, and subsequent operations with the Home Fleet before going to the Med in mid-Aug as a replacement for the again damaged Indomitable. She had been offered to the USN along with Vic at the end of 1942, and accepted by them, before the RN decided to send Vic instead.

The next carrier to serve in the IO was the escort carrier Battler which arrived in Oct 1943, fresh from Operation Avalanche, to begin ASW and searches for German supply ships.

 

[AZRailwhale]

Somerville's carriers actually had a pretty good shot at sinking/crippling Hiryu and Soryu (Cardiv 2) on the late afternoon, evening of 5 April 1942. Cardiv 2 became detached from the main body of the KB and had Somerville flown off a strike towards their last reported position, then ~40 Albacores would have encountered Cardiv 2 just after sunset.

Somerville wasn't willing to risk launching a search/strike mission. He was under orders to not risk his forces against even a comparable force,

 

[RCAFson]

Somerville wasn't willing to risk launching a search/strike mission. He was under orders to not risk his forces against even a comparable force,

Sources for that?

Somerville's Report of Proceeding for 5 April 1942:

..."37. A destroyer was detached to search but was recalled when at 1655 a reconnaissance aircraft from Force A reported an enemy force of 5 "unknowns" in position 3-38N, 78-18E at 1600. There was then no indication of the course of speed of this unknown force, but it could be either;
(a). a new force previously unreported, or
(b). the force previously and last reported at 1004.
38. It is unfortunately necessary that no relief shadowers were sent off by the Rear Admiral Aircraft Carriers as soon as this report was received and that I omitted to obtain confirmation from Rear Admiral Aircraft Carriers that relief shadowers had been sent. (n.b. in text "shadows" pen and ink corrected to "shadowers" in both cases.) At 1700 I received a report from Colombo that there were indications of enemy aircraft carriers steering 230 degrees at 24 knots from an unknown position at 1400.
39. This was thought to be subsequent to the attack on the cruisers and my deductions from this enemy move was as follows.
40. If he held on this course he would be at 0400 in a position to deliver a night air attack on Addu Atoll. This seemed quite a possible course of action. In any case it was necessary for Force A to keep clear to the southward and for Force B (estimated to be 135 miles astern in position 0-12N, 75-15E at 1700) to steer southward so that Forces A and B could close for supporting action at daylight the following morning (6th April). It as also necessary for Force B to steer to southward to keep clear of the enemy carrier force should it be proceeding to attack Addu.
41. At 1726, therefore Force A altered course to 210 degrees at 18 knots and a signal was made to Vice Admiral, 2nd in Command and to DORSETSHIRE to steer south, though by this time I entertained grave fears concerning the fate of the two 8" cruisers. As I had received no signal from them that they were being attacked I felt it was possible they had escaped and were maintaining W/T silence.
42. At 1800 I received a signal from Rear Admiral, Aircraft Carriers, stating that reconnaissance aircraft reported the estimated enemy's position 20 degrees 120 miles at 1710. This position was very close to the previously reported 1600 signal. The enemy's course had not been given in either of these reports, but the positions fitted in well with the course received in paragraph 38.
43. At 1817 a further signal was received from Rear Admiral, Aircraft Carriers, adjusting the 1600 position of the enemy force, amplifying it to include 2 carriers and 3 unknown vessels and giving the course as northwest. This was the first indication I had of an enemy course to the northwest.
44. I immediately ordered Force A to alter course to 315 degrees and instructed Vice Admiral, 2nd in Command to conform. These movements had the object of keeping Force A within night air striking distance of the enemy force, trusting to an A.S.V. search to locate the enemy, and to being Force B within supporting distance should it be necessary to retire in that direction. A dawn rendezvous was arranged with Force B in approximate position 3N, 75E.
45. As no news had been received of DORSETSHIRE and CORNWALL, the presumption was that they had been sunk.
46. At 1930 a night search with A.S.V. aircraft commenced to cover the section 345 degrees to 030 degrees to a depth of 180 miles. Nothing was located by this search."...

 

[AZRailwhale]

Sources for that?

Somerville's Report of Proceeding for 5 April 1942:

..."37. A destroyer was detached to search but was recalled when at 1655 a reconnaissance aircraft from Force A reported an enemy force of 5 "unknowns" in position 3-38N, 78-18E at 1600. There was then no indication of the course of speed of this unknown force, but it could be either;
(a). a new force previously unreported, or
(b). the force previously and last reported at 1004.
38. It is unfortunately necessary that no relief shadowers were sent off by the Rear Admiral Aircraft Carriers as soon as this report was received and that I omitted to obtain confirmation from Rear Admiral Aircraft Carriers that relief shadowers had been sent. (n.b. in text "shadows" pen and ink corrected to "shadowers" in both cases.) At 1700 I received a report from Colombo that there were indications of enemy aircraft carriers steering 230 degrees at 24 knots from an unknown position at 1400.
39. This was thought to be subsequent to the attack on the cruisers and my deductions from this enemy move was as follows.
40. If he held on this course he would be at 0400 in a position to deliver a night air attack on Addu Atoll. This seemed quite a possible course of action. In any case it was necessary for Force A to keep clear to the southward and for Force B (estimated to be 135 miles astern in position 0-12N, 75-15E at 1700) to steer southward so that Forces A and B could close for supporting action at daylight the following morning (6th April). It as also necessary for Force B to steer to southward to keep clear of the enemy carrier force should it be proceeding to attack Addu.
41. At 1726, therefore Force A altered course to 210 degrees at 18 knots and a signal was made to Vice Admiral, 2nd in Command and to DORSETSHIRE to steer south, though by this time I entertained grave fears concerning the fate of the two 8" cruisers. As I had received no signal from them that they were being attacked I felt it was possible they had escaped and were maintaining W/T silence.
42. At 1800 I received a signal from Rear Admiral, Aircraft Carriers, stating that reconnaissance aircraft reported the estimated enemy's position 20 degrees 120 miles at 1710. This position was very close to the previously reported 1600 signal. The enemy's course had not been given in either of these reports, but the positions fitted in well with the course received in paragraph 38.
43. At 1817 a further signal was received from Rear Admiral, Aircraft Carriers, adjusting the 1600 position of the enemy force, amplifying it to include 2 carriers and 3 unknown vessels and giving the course as northwest. This was the first indication I had of an enemy course to the northwest.
44. I immediately ordered Force A to alter course to 315 degrees and instructed Vice Admiral, 2nd in Command to conform. These movements had the object of keeping Force A within night air striking distance of the enemy force, trusting to an A.S.V. search to locate the enemy, and to being Force B within supporting distance should it be necessary to retire in that direction. A dawn rendezvous was arranged with Force B in approximate position 3N, 75E.
45. As no news had been received of DORSETSHIRE and CORNWALL, the presumption was that they had been sunk.
46. At 1930 a night search with A.S.V. aircraft commenced to cover the section 345 degrees to 030 degrees to a depth of 180 miles. Nothing was located by this search."...

He had enough radar equipped aircraft that he could have launched a search/strike mission. The only risk would have been operational losses from bad landings. At best he could find the IJN, at worst he could write off a couple of Albacores or Swordfish and burn some a gas. American commanders launched strikes on less data than Somerville had.

 

[RCAFson]

First you say:

"Somerville wasn't willing to risk launching a search/strike mission. He was under orders to not risk his forces against even a comparable force,"

Then when confronted with the truth you come up with this:

He had enough radar equipped aircraft that he could have launched a search/strike mission. The only risk would have been operational losses from bad landings. At best he could find the IJN, at worst he could write off a couple of Albacores or Swordfish and burn some a gas. American commanders launched strikes on less data than Somerville had.

geez...