April 1942. Fleet Returns to Japan Early

[Carl Schwamberger]

Kinda winging this one. Any experts on Japanese fleet deployments are welcome to provide info.

After Op C part of Nagumos fleet was returned to Japans ports to prepare for the next set of operations.

1. What ships returned to Japan & which ports did they return to?

2. Japanese naval intelligence warned of US carrier activity in the north Pacific & of the possibility of a carrier raid on the home islands. Given this warning what changes might there have been to returning fleet elements port assignments? For this I have to note the only practical measure the Japanese naval commanders did in response to the warning was to deploy a second picket line 300nm further east @ 600nm from Japan. Is that likely to change?

3. Had Nagumos fleet executed Op C a few days earlier & parts returned to Japan 24 to 48 hours before the execution of the USN raid would any elements been exposed to US attack?

4. I am looking at the damage to the submarine tender Taigei undergoing conversion to a light carrier (Ryuho). Most sources state the 500lb bomb hit damage delayed the converion by some six months. Would a similar hit on any of the fleet carriers have caused a similar delay in combat readiness?

[ChristopherPerrien]

Not much "what if" here. According to the TROM's at Combined Fleet/WW2DB , Only the Akagi appears to have been schedule to go Yokosuka first and went there, The rest went to Sasebo(Kaga,Hiryu) or Hashirajima(Soryu) or Op-MO(2 Shokaku's), . 1 B-25 went to Yokosuka. Personally I think the Akagi could have shrugged off one 500 lb GP hit, Given she would have had all ammo secured, no avgas in lines , no readied planes, and tied off in a navy base with good facilities. Maybe that B-25 could have travelled lengthways and maybe got more than one hit , who knows. But I think at the time it was considered 500lb GP bombs were marginal for seriously damaging active capital ships. http://pwencycl.kgbudge.com/B/o/Bombs.htm- puts it at about 6-7 weeks for repairing one serious 1000lb hit

[Carl Schwamberger]

Yes, it looks like the Akagi would be the only other target. Would the US pilot see it as a better target than the Taigei? Tough to say. Damage has so many variables in terms of where the bomb hits, how it is fuzed - delay or quick (?) and if a bunch of flammable construction material is at hand... If the Akagi is not undergoing any repair/refitting then it is much safer. Worst case is a bomb with delay fuse reaches the sole boiler pressurized for 'housekeeping, but as the physics joke goes; what are the odds of that happening?

I was reviewing some notes concerning air attacks on ships 1940-1942 & saw the entry for the Taigei, which caused the wheels to turn which led to here.

[mescal]

3. Had Nagumos fleet executed Op C a few days earlier & parts returned to Japan 24 to 48 hours before the execution of the USN raid would any elements been exposed to US attack?

The fleet was still SW of Formosa when they heard of the Doolittle Raid (precisely W of Bashi Channel, about to enter Formosa Strait).
That's around 1 400 nm away from Yokosuka, not taking any zig-zag pattern into account. At 15 knots, this means more than 3 and half days.

Thus to have the fleet back at home at the time of the Doolittle Raid, you need to make a significantly earlier raid in the Indian Ocean.
But in this case, you may well have an engagement with the British Eastern Fleet - Somerville had taken position to intercept such a raid on or about April 1st.
In such case, there is a strong probability that the situation butterfly away from the OTL.

4. I am looking at the damage to the submarine tender Taigei undergoing conversion to a light carrier (Ryuho). Most sources state the 500lb bomb hit damage delayed the converion by some six months. Would a similar hit on any of the fleet carriers have caused a similar delay in combat readiness?

Here is a picture of the damaged Taigei :
http://www.ijnwarship.com/IJN%20Lore/Vo ... -04-18.htm

The reference to the "six months" delay comes from the fact that Ryuho was commissionned in the IJN as a carrier six months after the raid.
I don't buy it that a single hit by a 500lbs bomb led to six months of delay. Especially as there was not catastrophic event associated (like magazine detonation, incontrolable fires etc).
The bomb hit definitely lengthened the conversion work, but not by 6 months.

Regarding the possible effects on another carrier, the main question is whether said carrier would be in drydock or afloat.
If afloat, a lucky hit which would go all the way down and rupture her hull underwater could be very dangerous, because she wouldn't be at any degree of combat watertightness (think USS California), and perhaps not fully manned, which would hinder counterflooding.
OTOH, if she's in drydock, this danger disappears. And the second danger (magazine explosion of avgas fire) may well also disappear if she is de-ammunitionned before entering the dock (I do not know the IJN procedures regarding ammunition/de-ammunitioning when under repair.)

[Carl Schwamberger]

3. Had Nagumos fleet executed Op C a few days earlier & parts returned to Japan 24 to 48 hours before the execution of the USN raid would any elements been exposed to US attack?

The fleet was still SW of Formosa when they heard of the Doolittle Raid (precisely W of Bashi Channel, about to enter Formosa Strait).
That's around 1 400 nm away from Yokosuka, not taking any zig-zag pattern into account. At 15 knots, this means more than 3 and half days.

Thus to have the fleet back at home at the time of the Doolittle Raid, you need to make a significantly earlier raid in the Indian Ocean.

Alternately Nagumo acquires a reason to end the raid a few days earlier. Some inteligence or other leads him to decide sinking a pair of cruisers and a largish bag of merchant ships is good enough, so he turns home on the morning of the 6th vs the 9th or 10th.

4. I am looking at the damage to the submarine tender Taigei undergoing conversion to a light carrier (Ryuho). Most sources state the 500lb bomb hit damage delayed the converion by some six months. Would a similar hit on any of the fleet carriers have caused a similar delay in combat readiness?

Regarding the possible effects on another carrier, the main question is whether said carrier would be in drydock or afloat.

The Akagi was the only carrier sent to Yokosuka, & it was not drydocked.

If afloat, a lucky hit which would go all the way down and rupture her hull underwater could be very dangerous, because she wouldn't be at any degree of combat watertightness (think USS California), and perhaps not fully manned, which would hinder counterflooding.

There is the golden bullet outcome, where the bombs fuze delays until the thing goes off on a pressurized boiler. But as the physics joke goes: What are the odds of that happening.