Dive bombers to Ceylon 1942 (1 Viewer)

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When dive bombers are sighted they actually do mate
 
The SBD never carried more than a 1000lb bomb load during carrier based missions. Even the SBD-5 had to reduce fuel load from 254 to 165USG to carry a 1600lb bomb and the rated combat radius was reduced from 240nm (1000lb bomb) to 95nm. The SBD-3 had a 1000hp at TO engine and the SBD-5 (1943) had 1200 and the final variant the SBD-6 had 1350hp at TO. The SBD-6 only operated from land bases, AFAIK. At Philippine Sea the USN strike aircraft relaxed the normal allowances for climb and loiter during formup and landing to extend the combat radius.

The SBD-5 could carry two DTs and a 500lb bomb for extended range scout/strike missions. The Swordfish/Albacore could carry a torpedo or ~1700lb bomb load and an internal 60/100IG aux tank. An external 60 or 108IG tank could be used to extend range for DB strike or scout missions.
 
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Steamed_Banana said:
Strike radius for SBD was effectively 175 miles with a 1,650 lb or 1,000 lb bomb on the centerline and up to 650 lbs more bombs in the wings,
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I really wish many people writing books and internet pages would just forget about the US 1600lb bomb. There has been a greater tonnage of ink spent on it than the tonnage of bombs that were actually dropped.
It had two things going for it in WW and in the many years after.
1. Due to being an AP bomb it was skinny (lots of steel and not much HE) and would fit anywhere a 1000lb bomb would. The bomb lugs were the same size spacing as a 1000lb bomb.
2. It sounds cool to say your plane can hold X number of 1600lb bombs.

After that it is all down hill, very steeply.
Unless you need to punch through 5 in of steel or a lot of concrete it doesn't do much. It needs to be dropped from high (for dive bombers) altitude so accuracy is not good.
Most of the US Essex class carries only carried 20 max in the magazines compared to several hundred 1000lb bombs. Shore bases probably got none.
In All of Europe (or just NW ?) they only dropped in the low 200s for the entire war. Does anybody really think that P-61 night fighters were flying around dropping 2-4 1600lb AP bombs? The spec sheets say it could carry them
The 650lb under wing load for the SBD is another spec writers dream. The US didn't have any 325lb bombs, either army or navy. They had 325lb depth charges. Now find a mission that requires carrying both depth charges and a large AP bomb at the same time? You can't drop them at the same time and hit the target, the flat nosed depth charge is not going to follow the same trajectory.
USN did, at times, put impact fuses into the depth charges and use them as blast/fragmentation bombs. Bomb shortage? Using them under SBDs doing anti sub patrol makes a lot a of sense, but not in combination with the famous 1600lb AP bomb.
The USN got rid of their 300lb/250lb bombs fairly early on. No room in the magazines. If you needed more than 100lb bomb go to the 500lb bomb.
 

So what? it's the spec. And in the Ceylon scenario, or the actual deployment with non-US forces, USMC, USAAF etc., they had access to bombs made by a wide array of other countries. US fighter bombers routinely carried Russian, British, and captured enemy / Axis produced bombs at various points. And yes things like depth charges were used against ships like during the Battle off Samar by TBFs.

1600 / 325 lb is the capacity, how often they carried the load in a given circumstance with the US Navy is fairly irrelevant. Normal load was 1,000 and 500 lbs bombs though they did carry wing bombs sometimes, and even things like rockets and yep depth charges.
 
Steamed_Banana said:
When dive bombers are sighted they actually do mate
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It takes some time to get from 18 to 30+ kts. You're not just stepping on the gas pedal and getting pushed back into your seat. It's common knowledge that the highest reaches of a ship's speed take proportionally longer to reach, i.e. going from 10 kts to 20 might take thirty minutes (broad numbers to make the point, not being exact for any one ship), while going from 20 kts to 30 might take yet another 45 minutes, and then going from 30 to 34.5 might take another thirty minutes.

You can thank physics for the phenomenon, and Drachinifel for making the point in one of his Drydock episodes.
 
The Shokakus could achieve 26 knots on their separate cruise turbines producing 50,000shp and the props turning at 204rpm. That was considered plenty to allow aircraft to take off even in light winds.

To get any more speed meant using the main turbine set (HP/IP/LP turbines) to produce the full 160,000shp for their max speed of 34.5 knots with the props turning at 300rpm.

Trial data:-
Shokaku - 34.37 knots using 161,290shp at 307rpm at displacement 30,003 tonnes.

Zuikaku - 34.58 knots using 168,100shp

Warship 2015 "The Aircraft Carriers of the Shokaku Class" by Hans Lengerer.
 

I do realize it takes a while to fire up boilers, but I also believe that ship captains and admirals have a sense of when they are about to come into serious risk of being attacked. Like say, if you had just launched strikes on an enemy base that was in range, or when you had spotted enemy carriers in bomber range within a few hours. Or when one of your strike groups reported seeing enemy aircraft.

I also know that flank speed and wild maneuvering seemed to be a key factor in the survival of aircraft carriers during the war, as they were often able to dodge bomb hits when they weren't attacked by surprise, especially against relatively small numbers of bombers. I don't know the exact speed of Shokaku and Zuikaku in the various battles they were in though I suspect that data is available.



This is Zuikaku and Zuiho maneuvering under bomb attack during the Battle off Cape Engano on 25 Oct 1944. A Helldiver can be seen diving in the lower left.
 

The problem is that accelerating 23,000 tons through water is not a machinery matter. It is a problem of physics.

A strike force heading for its target may be cruising at 22 kts, and do its final dash at 26-28 kts, but that is offensive planning. If that same task force gets attacked at a point when it is at 60% of its possible speed, that last 40% is actually the hardest part to accelerate. That's because the inertia carried in such tonnages retards acceleration itself. It's not about boilers. Even while cruising, ships will have all boilers lit unless there's a maintenance issue.

The problem lies in applying that energy to overcome the inertia of a massive object, along with minor issues like friction-loss. A lighter object is quicker to both accelerate and decelerate; a heavier object is slower in both regards. Anyone who has driven a heavy truck knows this.
 
Steamed_Banana said:
I guess.. what other time would you ever use your top speed of 34 knots if not while the dive bombers were attacking?
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While you're running in to the launch-point and planning to get out before daybreak. See the American raid on Rabaul in late 1943 for a good example. Top speed is dash speed rather than combat speed, in most cases.

You'll need forewarning to get to top speed before the bombs drop. The last five knots of a carrier's speed is the hardest to comp, for aforementioned reasons.
 
Steamed_Banana said:
I guess.. what other time would you ever use your top speed of 34 knots if not while the dive bombers were attacking?
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By way of example take a look at US TF operating instructions laid down in 1943 and applied to the end of the war and beyond.

They laid down details of formations to be adopted and procedures to be used. TG speeds were generally based on a speed range of 15-25 knots set by the fleet commander as circumstances dictated. To maintain TG integrity the whole force maneuvered as one single body dictated by the speed of the slowest ship. A South Dakota battleship had a max speed of 27 knots on a good day. Then the escorting destroyers needed a margin above TG speed so they could maintain position as the TG manoeuvered. Although they had a theoretical speed of 36 knots you could knock off a few knots as their full load displacement increased with more guns and radars.

So you had Essex and Independence class carriers capable of 33 knots but there was little need for that.

If a carrier needed to operate its aircraft outwith the regular TG operating cycle, the orders were clearly laid down. It left its designated position in the TG and positioned itself as far downwind as possible, turned and ran into wind at whatever speed it required to launch / land its aircraft as quickly as possible. Then it dropped back into its designated position. BUT most importantly, its movements ALWAYS remained within the outer ring of escorts.

If a TG came under attack the whole formation was changed with the rings of escorts moving in closer to the carriers to increase the AA cover. It could not have ships manoeuvering wildly thereby increasing the risk of collisions.

The IJN also learned lessons from 1942 actions, adopting tighter circular TG formations in 1943.

Looking at the KB in Operation C the 5 carriers had a variety of max speeds. Akagi 31 knots, Soryu & Hiryu 34 knots, Shokakus 34.5 knots but the Kongos were good for only 30 knots. And those speeds were on a good day. Having been at at sea for months there would have been an accumulation of marine growth knocking a few knots off each ship.

When operating aircraft in WW2, carrier only needed about 30 knots of wind over the deck. Zero wind conditions were rare.

Fuel consumption was also an issue. Fuel burn increased dramatically with speed. And when you had a limited oiler fleet available it became a major factor especially for the escorting destroyers.

Also bear in mind that when the major classes of WW2 carriers were designed, multiple carrier TG were a thing of the future ( only the RN had experimented with them in the early 1930s). Japan only adopted them in April 1941 and the US in 1942.

So in summary there was generally little need for such high speeds in practice in any of the navies.
 
Sorry I wasn't more clear. It was a general rant, not aimed at you.
But yes it is somewhat relevant, in that it seems nobody as been able to come up with an action report where the SBDs ever used the 1600lb in action. Which means that the SBD 2250lb bomb load was never used in action. Ever. By any version of the SBD.
Use of the 325lb depth charge was fairly common. Once it was adopted and issued.

The best way for the British to get either the US 1600lb bomb or even the MK 17 325lb depth charge to Ceylon in early April 1942 is with a Tardis. Granted it was close.
But timing is different than actually using them in the manner some people think.

Many air forces used non-standard bombs. But it usually took a few weeks to do it. If the bomb lugs (cast into the bomb body) do not line up with the racks in use there are ways around it. Some air forces used strap fastened around the bomb with a properly spaced lug. Some air forces may have used a strap around the bomb fastened to the rack and the strap came apart (came off the bomb) as it was dropped. It can depend on work shop facilities. But such work arounds do need to be tested.
But that was not the issue here either.
 
EwenS said:
So in summary there was generally little need for such high speeds in practice in any of the navies.
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Some navies may have relied more on speed and maneuver than others and/or changed with time?
Just asking but the US and the British may have put more faith in their AA batteries at times. This may depend on which ships were in a particular force and when.
Wild maneuvering may have worked well in small groups of ships but it not only increases the risk of collision, it increases the risks of friendly fire incidents, especially with larger groups of ships.
Wild maneuvering may also increase the risk of a submarine getting off some shots as the anti sub screen is both no longer able to use sonar and is getting further apart.
 
So when does it get to full speed? If not while under bomber attack (or when anticipating imminent bomber attack) i really can't imagine any other time. What am i missing here?
 
Steamed_Banana said:
So when does it get to full speed? If not while under bomber attack (or when anticipating imminent bomber attack) i really can't imagine any other time. What am i missing here?
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In windless conditions to launch a deck load strike. The IJN never used flight deck catapults on their carriers, so high speed was specified to aid in carrier ops, as was the need for light weight aircraft.

The speed chosen when under attack had to also factor in the ability of screening ships to provide AA protection ( however circular AA formations were not used in the KB even at Midway) and the best speed for manoeuvre which wasn't necessarily maximum speed.
 

IJN doctrine for defending carriers against air attack -- aside from the obvious CAP in place for active defense -- was, yes, to speed up and turn the hell out of your ships. They weren't dummies; they knew their AAA was not up to snuff, which is why they designed, built and installed that really handy 3.9" twin-turret ... too little, too late, but a good effort nonetheless.

But to my knowledge, there was no doctrinal shift from "making a plate of spaghetti" to "formate, lock in, and rely on gunnery". Probably because they didn't have any good gun in any good numbers, never developed a VT fuse, never managed a 5" with a respectable rate of fire.

I know that with Ten-Go the supporting ships compacted upon Yamato specifically for AAA help, but even then, I think if you put in an equable American force -- one Iowa, one Cleveland, and six or eight Fletchers -- the American ships would probably still wind up sucking seawater, but there'd be a lot more dead aviators. The Japanese didn't resource shipborne air defense nearly so much proportionally. They simply couldn't. Dodging was pretty much the only realistic option, if you didn't have air-cover.

By 1944, that wasn't the case with USN or RN ships. Between improving radar, maturing CICs, VT fuses, those little 4.5" pancake turret the Brits liked and the 5"38s festooning American ships, and you get a Mk 37 director, you get a Mk 37 director [insert Oprah .gif here], an Allied carrier task force in the Pacific was probably the most dangerous airspace in the world, and I include deep Germany in that.
 
Steamed_Banana said:
So when does it get to full speed? If not while under bomber attack (or when anticipating imminent bomber attack) i really can't imagine any other time. What am i missing here?
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Approaching and leaving the launch-point. You want to minimize your exposure to hostile attack. Under hostile attack, of course you speed up, so far as you can.

The other thing is that a higher top speed gives you (usually) a higher efficient cruising speed, and what that means is that even if you never need to hit topmost speed, the higher cruising speed supports the primary quality of an aircraft carrier -- mobility. A 34 kt ship that can cruise efficiently at 24 kts is more mobile than a 30kt ship that can cruise easily at 20. That doesn't sound like much, but in wide oceans with days of travel, four nautical miles per hour adds up fast. On a four-day mission that's about 500 miles.

The top speed stuff is Top Trumps stuff for ships, I think. The Japanese built-in high top speeds for their ships precisely because the IJN's mission looked out into the vast expanses of the Pacific and understood that high speed was needed, and plant that can kick 34 kts wide-open can do a good job at 25 kts. Americans did the same, except for the Standard battleships.
 
Production of the US 1,600lb AP bomb only began in early 1942 with service introduction by the USN about May. The 1,000lb AP bomb entered service in Sept 1942.

Swordfish, Albacores & Barracudas were designed to carry a torpedo or drop tank under the fuselage but not bombs. From 1940 they could also carry mines, but they were similar to torpedoes and use that suspension equipment. Bomb loads were carried on underwing racks that could be removed when not required. They didn't use the British 2,000lb AP bomb introduced to service in 1940.

The US 1,600lb bomb was made available to the RN from late 1943. It was first used against the Tirpitz in Operation Tungsten on 3rd April 1944. But the Barracudas had to be modified to allow it to be hung from their torpedo fixings. Photo here

Operation Tungsten - Wikipedia

en.wikipedia.org

And anyway you don't need a 1,600lb AP bomb to wreck a carrier or even a 1,000lb AP one.

Britain didn't need US airborne depth charges. It had its own. The 450lb Mk.VII airborne DC was adapted from the normal shipboard DC in 1941 following the failure of the pre-war 100lb AS bomb. The 250lb Mk.VIII & XI replacements were designed in 1941 to enter service from 1942 and became the standard British airborne DC.
 
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