Why the Skua Only Carried a 500lb Bomb

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elbmc1969

Senior Airman
513
348
Feb 16, 2019
One of the Skua's weaknesses was that it could only carry a 500lb bomb, which was inadequate against battleships, and provided less destructive power against (Japanese) carriers than the 1000lb bombs that were widely used by other dive bombers. Was the 500lb bomb the product of technical limitations, deliberate doctrinal choice for naval warfare (perhaps torpedoes are for killing ships?), the Air Ministry specification for a non-doctrinal reason, or something else?

I believe I have found the answer, somewhat in plain sight.

According to Neville Jones' The Beginnings of Strategic Air Power: A History of the British Bomber Force, 1923-1939, in July of 1932 the Chief of the Air Staff decided that no bomb larger than 500lbs would be produced. This was despite the fact that operational experience had shown the need for larger bombs, that Trenchard had stated in 1923 that 4000lb bombs would eventually be needed, and that a 1000lb bomb was in trials in 1930.

In 1935, a sub-committee of the Bombing Committee reaffirmed that no bombs over 500 lb should be produced.

Because the Skua was designed to Specification O.27/34, the 500lb limit was in effect, so there was no prospect of a larger bomb being introduced, even Blackburn had thought about going beyond the specification.

To make this even more tragic, early in 1939 the Air Staff called on Bomber Command to plan to attack enemy warships, and specifically to sink at least one German battleship. Beyond the Commander-in-Chief replying that he did not believe that his forces could hit enemy warships, the naval staff produced a paper "expressing the strongest doubts" that any kind of warship could be destroyed by the RAF's 500lb bombs. In other words, the Air Staff had simply ignored the possibility that the RAF might be called on to attack ships by bombing (presumably, they mentally assigned this role to torpedo bombers, which was not totally irrational, but would be impossible with land-based aircraft based in the UK). The contrast with the USAAC, which was obsessed with attacking battleships with high-altitude bombers, and with the IJN, is striking. This provides an example both powerful and subtle of the damage done to the Fleet Air Arm by making it part of the RAF.

tl;dr The RAF wasn't going to buy bombs bigger than 500lbs, so there was no point in designing a dive bomber to carry anything larger.


PS--The belief that more small bombs were better against industrial targets than a few large bombs also influenced the design of the Fairey Battle. Placing four 250lb bombs inside this wings as the primary armament make a thick wing necessary to accommodate them, regardless of the choice of wing profile for takeoff distance and range. The thick wing limited the maximum speed of the Battle after it had dropped its bombs. I cannot make a meaningful statement about the Battle's maximum speed and range if it had a thin wing and carried a single 1000lb (or 500lb) bomb externally.

PPS--The conversation around bombing ships was part of the "Oh, dear, the entire concept of the RAF was that our bomber forces would hit first, hit hard, and keep hitting until we win, but now we don't think that we can pull it off and we're afraid that if we do start bombing, the Luftwaffe will attack our airfields and annihilate Bomber Command, even though we don't think that there's any way that Bomber Command could attack Luftwaffe airfields with any effect, and the government is afraid that if we start bombing, the Germans will retaliate against London, and we agree that it's a risk and that the UK population might crack first and none of our thinking right now is internally consistent" period.
 
I am sure that is part of it.

Another part was the engine/propeller choice. Trying to lift a heavier bomb without restricting fuel load would have been very difficult. About 830hp for take-off so even if the RAF could come up with a heavier bomb the Skua would have trouble lifting it.
Not helped by the 2 pitch prop.

Now if we can figure out the whole SAP bomb with 90 pounds of HE as the ONLY bomb available (or only big one) reasoning we have the complete story.
 
With the thick wing still not being recognised as a problem designers, such as Mitchell with the 4 engined Supermarine heavy bomber, took advantage of the RAF standard 250lb bomb to put them in the wings and save fuselage space. Bomb cells not only in the Battle but also the Stirling, Whitley and Halifax. In Supermarine's case the entire bomb load was in the wing bomb cells.
 
The Skua was designed and introduced specifically to knock out IJN carriers and I think it was felt that a 500lb bomb was sufficient for that. I suspect the IJN came to similar conclusions, hence the 550lb limit on the Val1 and Val2. We also have to remember that most RN carriers had relatively short flight decks so low wing loading was a critical concern,
 
Another part was the engine/propeller choice. Trying to lift a heavier bomb without restricting fuel load would have been very difficult. About 830hp for take-off so even if the RAF could come up with a heavier bomb the Skua would have trouble lifting it.
Not helped by the 2 pitch prop.
The notably heavier Roc could get off the deck with the same 500lb bomb load, so the Skua clearly could have gotten up with the same TO weight.

The two-pitch prop was not a problem for take-off, since it had an optimal setting for take-off and initial flight, and could be manually adjusted for optimal climb (which wasn't that much of a difference).
 
The Skua was designed and introduced specifically to knock out IJN carriers and I think it was felt that a 500lb bomb was sufficient for that.
While that may be true, the FAA also had no doctrinal choice because of the restriction on bombs.

Also, the Skua was clearly going to have to fight non-carrier German warships. Even if a 500lb bomb was sufficient against a heavy cruiser, a 1000lb bomb was a vastly better choice.
 
The two-pitch prop was not a problem for take-off, since it had an optimal setting for take-off and initial flight, and could be manually adjusted for optimal climb (which wasn't that much of a difference).
Both the Skua and the SBD use props with 20 degrees of pitch change, and that may be all they needed. We are not talking about 350mph aircraft after all.

As a dive bomber having manually adjust the propeller pitch as you were climbing is better than having to choose A or B (and there really wasn't much choice, You were going to over rev the engine if you kept in in shallow pitch). However trying to adjust the pitch when acting as a fighter/interceptor seems like unnecessary work for the pilot.

British also had several different carriers of different speeds and flight deck lengths. Perhaps they hoped the smaller, slower carriers would fade from view as the new construction carriers took their place.
It is tough being among the leaders and then going to war when the planned for replacements are running late. In an Ideal world the Skua would have shown up at the end of 1937, been lauded for showing the RN how to deal with retractable gear mono-planes for about 3 years and been replaced before war broke out in 1940/41. That is not how things worked out but that is not really the Skuas fault (or it's design team).
 
It's impressive all the things those teams got right in those transitional times. The Skua, the TBD, and even the Buffalo which was an innovative design to restrictive requirements, poorly executed.
But that wind screen. Oy.
Remember that the Skua was more a contemporary of this.
621px-Northrop_BT-1_VB-6_1939.jpg

Than the SBD. Douglas got a "redo" on this to get the SBD.
Blackburn never got a "redo".
And the Skua didn't try to turn over on it's back when it stalled during landing.
Yes Douglas fixed that.
 
British also had several different carriers of different speeds and flight deck lengths. Perhaps they hoped the smaller, slower carriers would fade from view as the new construction carriers took their place.
In 1937/38 Argus was converted to a Queen Bee carrier and was considered an auxiliary not a carrier.

In May 1939 the Admiralty looked forward to its carrier deployment in 1942 in the event of peace, war in Europe and war against Japan. By then it was anticipated that the first 6 armoured carriers would be in service (more were then planned). The plans for the old carriers were as follows:-

Argus & Eagle get no mention at all in any scenario. Argus probably due to her changed status. By 1942 Eagle's boilers were expected to need replaced so, given her other limitations, was probably not considered worthwhile giving a major refit to.

Peace
Furious, C&G & Hermes all in Reserve.

War
Furious was to be a training carrier in home waters.

C&G were to be active with air groups of only 24 aircraft each. Taken along with their proposed locations, it looks like they would be reduced to the trade protection role. European war = Kingston & Freetown. Far East war = Trincomalee and Singapore.

Hermes, with 12 aircraft would have been in the western Atlantic, either in Halifax or Kingston.

Having decided on one carrier, Indefatigable, for the 1939 Programme, at least one more was being planned for each of the 1940 & 1941 Programmes. Much discussion took place around the composition of each Programme.
 
While that may be true, the FAA also had no doctrinal choice because of the restriction on bombs.

Also, the Skua was clearly going to have to fight non-carrier German warships. Even if a 500lb bomb was sufficient against a heavy cruiser, a 1000lb bomb was a vastly better choice.
Again, the IJN went with a 550lb limit on the Val1 and Val2; why?

The USN had modern carriers at Midway, that could make ~32 knots and had 800ft flight decks, yet about 1/2 the SBD sorties carried 500lb bombs because of the TO characteristics of the SBD versus the expected wind conditions.

A bomb larger than ~500lb would have been problematic on a Skua and the prewar RN carrier fleet, and even on the wartime Implacable class.
 
The USN had modern carriers at Midway, that could make ~32 knots and had 800ft flight decks, yet about 1/2 the SBD sorties carried 500lb bombs because of the TO characteristics of the SBD versus the expected wind conditions.
The US expected to fly the planes off from a deck park using a lot less than 800ft, in fact under 400ft. The planes closest to the bow got the 500lb bombs and the planes with a little more room got the 1000lb bombs.
Summer in the tropics may give a bit longer take-off the "book" but a SBD with a 1000lb bomb and 100 gal was supposed to need 853ft zero wind. They may have stuck more fuel in them than that ;)

edit. The SBD vs the Skua is usually going to show the Skua at a disadvantage. The Skua had under 85% if the power for take-off. and that is for the SBD-2,3,4. The Skua had about 70% of the power of an SBD-5 but then they stopped making Skuas 3 years before the SBD-5 was built.

Anybody want to talk about how much better a Spitfire IX was than a P-40B? ;)
 
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Again, the IJN went with a 550lb limit on the Val1 and Val2; why?

The USN had modern carriers at Midway, that could make ~32 knots and had 800ft flight decks, yet about 1/2 the SBD sorties carried 500lb bombs because of the TO characteristics of the SBD versus the expected wind conditions.

A bomb larger than ~500lb would have been problematic on a Skua and the prewar RN carrier fleet, and even on the wartime Implacable class.

A big reason about half the SBDs carried 500-lb bombs was actually mission. A USN carrier in 1942 carried two squadrons of SBDs, one tasked with attack, one tasked with scouting and opportunity strikes. The Scouting squadron generally carried 500-lbers for range purposes. Attack bombers generally carried 1000-lb bombs, because, well, strike. But both squadrons could and did carry both sizes of bomb. The planes were themselves identical.

None of this was a result of flight-deck limitations so long as the air-park was handled with competence. Indeed there were missions when TBDs were stowed so that all SBDs could launch with 1000-lb bombs.
 
A big reason about half the SBDs carried 500-lb bombs was actually mission. A USN carrier in 1942 carried two squadrons of SBDs, one tasked with attack, one tasked with scouting and opportunity strikes. The Scouting squadron generally carried 500-lbers for range purposes. Attack bombers generally carried 1000-lb bombs, because, well, strike. But both squadrons could and did carry both sizes of bomb. The planes were themselves identical.

None of this was a result of flight-deck limitations so long as the air-park was handled with competence. Indeed there were missions when TBDs were stowed so that all SBDs could launch with 1000-lb bombs.
TF16's SBD loadout was a direct result of wind over deck (surface winds were 5 to 9 knots) vs required TO run based upon the deck load that had been planned for the 1st strikes on 4 June. Yorktown decided to use a smaller strike, that allowed for a pure 1000lb loadout.

"At the conference the Hornet flight leaders worked out the launch scheme and procedure for flying to the target. Because of the high number of aircraft involved, the launch would require two deckloads. The first would comprise the CAP fighters (eight F4Fs plus two standby), the ten escort fighters, and all thirty-four Hornet SBD dive bombers. Whatever room was left on the flight deck after all these aircraft were spotted could be given to a few of VT-8's TBDs. Half the dive bombers would carry one 500-lb. bomb apiece; the rest that could be spotted farther aft and with more deck space to work with were to get off with one 1,000-lb. bomb slung under each. After the fighters and SBDs had lifted off, plane handlers could bring out of the hangar the remainder of VT-8's fifteen TBDs. While the torpedo planes made ready to take off, the SBDs and their fighter escorts would begin the long climb to 20,000 feet. If time permitted, the SBDs and F4Fs would circle until the TBDs were ready to depart. Then they would cruise at 110 knots, while Waldron's troops were to climb to 1,500 feet and head out at 100 knots. Ring's high-level contingent hoped to maintain visual contact with the torpedo planes far below during the flight out." (Lundstrom).

The Skua had less power than the SBD, but it was lighter and had lower wing loading, so TO distance was probably pretty similar. However:

All 3 Yorktown class carriers had 800ft flight decks and were nominally good for 32 knots.

Glorious, Courageous and Furious all had ~550ft flight decks and could make about 28-29 knots.

Eagle had a ~630ft flight deck but could barely make 23 knots.

Ark Royal had a usable flight deck of about 700ft and could make 30-31 knots.

It's pretty clear from the above that if the USN was using the above carriers at Midway that the SBDs would all be carrying 500lb bombs to ensure that they could TO in the prevailing surface wind.
 
The Skua had less power than the SBD, but it was lighter and had lower wing loading, so TO distance was probably pretty similar.
This gets a bit tricky as the Skua didn't change much and the SBDs were all over the map. In part because of the scout mission. Early SBDs without protection grossed 8605lbs with 310US gallons of fuel (all internal) and NO bomb. With 180 US Gal and no bomb they grossed 7773lbs. There was room for a 500lb bomb, 180 US gal and to within about 100lbs of the Skua.
They could lift a 1000lb bomb and 100US gal (84 imp ?) and gross 8339lbs. Obviously rather short ranged.
Protection changed that, big time.
Crew protection was 212lbs.
Center section fuel tanks gained 232lbs.
Outer wing fuel tanks gained 218lbs.
Oil tank gained 30lbs.

Max fuel dropped to 260 US gallons.
With a 500lb bomb and 140 US gallons weight went to 8786 and the fan favorite with 1000lbs and 100 US gal went to 9031lbs.
Again this is from the early 1942 manual, there are data sheets that show 1600lb bombs and gross weight of over 10,000lbs. And this is before the SBD-5 shows up.
I don't know what they were using at Midway for weight because I don't know the fuel load.
 
This gets a bit tricky as the Skua didn't change much and the SBDs were all over the map. In part because of the scout mission. Early SBDs without protection grossed 8605lbs with 310US gallons of fuel (all internal) and NO bomb. With 180 US Gal and no bomb they grossed 7773lbs. There was room for a 500lb bomb, 180 US gal and to within about 100lbs of the Skua.
They could lift a 1000lb bomb and 100US gal (84 imp ?) and gross 8339lbs. Obviously rather short ranged.
Protection changed that, big time.
Crew protection was 212lbs.
Center section fuel tanks gained 232lbs.
Outer wing fuel tanks gained 218lbs.
Oil tank gained 30lbs.

Max fuel dropped to 260 US gallons.
With a 500lb bomb and 140 US gallons weight went to 8786 and the fan favorite with 1000lbs and 100 US gal went to 9031lbs.
Again this is from the early 1942 manual, there are data sheets that show 1600lb bombs and gross weight of over 10,000lbs. And this is before the SBD-5 shows up.
I don't know what they were using at Midway for weight because I don't know the fuel load.
SAC data for the SBD-3 with armour, SS tanks, full fuel (260usg) and a 1000lb bomb was 10466lb* vs 8228lb, 200usg fuel and a 500lb bomb for the Skua.

*SAC states 10400lb with 249usg but Lundstrom and combat reports indicate that full fuel load was actually used.
 
Thank you, I know it was changed, what I don't know is when (before Midway) and how/why.
They did some calculations and figured the plane wouldn't break at the higher weights or did test flights or just figured that after some of the fuel burned off everything would be OK?
 

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