Hap Arnold's Inconsistency

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Obtain Reel A2069 from USAFHRC. I would send but it is a massive pdf file to upload. G.Sinclair was kind enough to download a copy for me but it took two tries and 8 hrs on Wetransfer (IIRC).
pages 1-281 all of Boylon's sources for Droppable Fuel tanks. Look to February 24 1942 Arnold C/AS to Tech.Div. Wright Field ---->Technical Order to Increase Range and March 2 1942 Chidlaw to Tech.Div Wright Field "Develop Self Sealing Drop Tanks". Feb 28 was date of order to develop self sealing non-droppable tanks to extend range.
The first memo I saw concerning Deveopment orders by AAF were K.B. Wolfe to Chief, Exp. Eng. Wright Field 12-9-41 "Initiate Composition Belly Tank, metal is very expensive".
pages 1551-2038 are details/correspondence for FAREP, also major source for Boylon's USAF Study 136 Development of Long Range Escort Fighter.
 
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V-3420 production 1 in September 1940, 1 in December 1941, then 30 in 1943, 112 in 1944 and 9 from January to August 1945. Peak production 28 in October 1944.

Serials 43-46950/46951 for 2 XP-75 AC-33962 1 October 1943, then another 6 added, serials 44-32161/32166, all 8 accepted in March 1945
43-46950 completed 17 November 1943, delivered 27 March 1945
43-46951 completed 23 December 1943, delivered 24 March 1945
44-32161 completed 13 January 1944, delivered 27 March 1945 Washout
44-32162 completed 5 February 1944, delivered 26 March 1945
44-32163 completed 17 March 1944, delivered 27 March 1945 Washout
44-32164 completed 15 May 1944, delivered 26 March 1945
44-32165 completed 8 March 1945, delivered 24 March 1945
44-32166 completed 8 March 1945, delivered 24 March 1945

44-44549/47048 for 2,500 P-75A-1, AC-41011 7 June 1944, 6 actually accepted, 44-44549 to 44554, 2 each in November 1944, February and May 1945.
44-44549 completed 18 November 1944, delivered 30 November 1944 Crashed
44-44550 completed 18 November 1944, delivered 21 November 1944
44-44551 completed 22 May 1945, delivered 22 May 1945
44-44552 completed 9 February 1945, delivered 9 February 1945
44-44553 completed 9 February 1945, delivered 9 February 1945
44-44554 completed 22 May 1945, delivered 22 May 1945

Type to class 26 on 5 July 1945

44-44552 and 44-44553 to ATSC, rest to experimental.

XP-75 crash 8 April 1944, at Cleveland, pilot killed, structural failure
XP-75 crash 25 August 1944, at Cleveland, baled out, explosion?
P-75 crash 10 October 1944, in Florida, pilot killed, forced landing material? failure

RC-301 production reports, starting January 1943
January to March 1943, 2 XP-75 ordered under 1943 experimental program
No reports April to June 1943
July 1943, 2 XP-75 ordered under 1943 experimental program, 6 more under 1944 experimental program, order for 2,500 P-75 not contracted, on J program for fiscal year 1943.
November 1943, order for P-75 changed to P-75A
April 1944, order for 2,500 P-75A changed to Approved Letter Contract status, completion scheduled December 1945. XP-75, program scheduled order completion May 1944 except 4 are marked unscheduled
No reports May and June 1944
July 1944, order for 2,500 P-75A on Approved Formal Contract status, completion scheduled December 1945. XP-75, program scheduled order completion July 1944 except 4 of second batch are marked unscheduled
October 1944, production order becomes 30 P-75A, none accepted, completion date unscheduled, XP-75 aircraft marked shop completed but now no scheduled order completion date.
November 1944, production order becomes 6 P-75A, of which 2 have been accepted, completion date January 1946.
March 1945 XP-75 program complete, 4 out of 6 P-75A accepted, balance due.
May 1945 P-75A order complete.

As of April 1944 the USAAF Schedule was for around 5,800 B-29 and 1,200 B-32 to have been accepted by end 1945, along with the 2,500 P-75A. In reality just under 3,800 B-29 accepted by end 1945.

Angelluci and Bowers in The American Fighter credit the 2 XP-75 with 534 US gallons of internal fuel, the 6 XP-75A and P-75A with 638 US gallons, no mention of XP-75A in the production reports. The book order dates are 2 XP-75 10 October 1942, 6 XP-75A 6 July 1944, 2,500 P-75A 7 June 1942, with the P-75A order cancelled on 27 October 1944, XP-75 first flight 17 November 1943, XP-75A 15 September 1944.

The built in range says the P-75 was for B-29 and B-32 escort missions, arriving in numbers about the same time. Trying for B-29 range helped ensure it was a 1945 fighter even if development was smooth including the airframe short cut ideas. The prototype P-47 first flew in March 1941, it arrived in numbers in 1943. The P-75 range on internal fuel was significantly beyond that needed for B-17 and B-24 missions in Europe.

AFHRA reel A2069 size is a bit under 785Mb.
AFHRA search Air Force History Index
AFHRA order page https://www.dafhistory.af.mil/Portals/16/documents/home/AFHRA_EDRForm.pdf
 
wuzak said:
Bill, were the British Mustang Is fitted with provisions for drop tanks, and if so, was that a requirement by the RAF?
Click to expand...
No for NA-73/83/91. Yes, for the single A-36, the 50 P-51A and ALL Merlin Mustangs. That said, the racks were easily removable.

The 85gal tank was not delivered in Mustang III initially as RAF had no long range high altitude daylight escort requirement. All P-51D/K were delivered w/85gal tank save the few F-6 mods.

When the P-51C-10-NT last block was produced, NAA delivered all w/85gal fuse tank, which was not so easily removed, and few were stripped by RAF AFAIK.
 
US Archives Record Group 18 Entry 7 Box 5666. October 1942 report on fighter performance and armament. A group of production fighters were stripped to below operational weights to see what effect that would have. All fighters currently coming off lines with desert and winter equipment, slowing overall production down.

The stripped P-40E equalled the P-51 in level flight at 5,000, 10,000 and 15,000 and was greatly superior in climb and manoeuvrability. The standard P-38G equalled the standard P-47 in level flight speed at 30,000 feet and was superior in the turning circle and vertical manoeuvrability from 30,000 to 20,000 feet. The stripped P-39D1 excelled the stripped P-40 in speed and manoeuvrability especially in the rolling plane. The stripped P-38 excelled both the stripped P-39 and P-40 in speed and climb at all altitudes.

Idea for trials of 37mm M4 gun in P-38, author prefers replacing the P-38 20mm with a 0.5 inch machine gun, the machine gun being superior to the cannon from almost every angle.

"The board carefully considered an extract cablegram from General Spaatz, 8th Air Force, relative to the invulnerability of the B-17 type airplane to hostile 20mm fire. Other operations reports from the United Kingdom substantiated the basic extract cablegram and further indicated the ability of the B-17 type to withstand hostile 20mm fire and to successfully engage and destroy or disable enemy fighters. Colonel Gerhart and Major Peterson of the 8th Air Force elaborated on the reports available to the board and cited numerous examples which served to confirm the opinions from Great Britain."

Given its success it was assumed the enemy would produce a bomber at least as good as the B-17 at absorbing 20mm fire. To counter this the 20mm was no good, the 75mm too big. The P-38 with 1 or 2 T-20 37mm cannon and 1 to 3 0.50 inch machine guns had the required performance, 500 T-20 37mm guns should be available by January 1943. Of the experimental types the XP-58 nearly met all requirements, the XP-67 and 71 considered too vulnerable to fighters. Immediate action to produce the next generation bomber destroyer was recommended. Estimated delivery XP-58 June 1943, XP-62 December 1942 but will probably be cancelled, XP-67 November 1943, XP-69 July 1943, XP-71 June 1944.

Bomber Destroyers,
XP-58 with 4x37mm high velocity cannon, or 1x75mm and 2x37mm, also able to carry 2,000 pound bombs. Not available before April 1943.
XP-67 with 6x37mm
XP-71 with 1x75mm and 2x37mm
As well methods could include Air to air bombing, head on attack, proximity fused 1,000 pound bomb. Rockets with timed or proximity fuses, P-47 with 3 under each wing, tubes dropped after rockets fired.

0.5 inch with 7.5 seconds of fire 114 pounds (13.3 rounds per second at 2,700 feet/second), 20mm with 6 seconds of fire 193.2 pounds (10 rps, 2,450 ft/sec), 37mm M4 with 15 rounds (6.8 seconds of fire) 294.25 pounds (2.2 rps, 1,600 ft/sec), 37mm M1A2 with 7.9 seconds of fire 479.95 pounds (1.9 rps, 2,900 ft/sec). At 500 yards range the 0.5 inch has dropped 68 inches, the 20mm 70 inches, the M1A2 92 inches the M4 185 inches. The T-20 was based on the M1A2, belt feed, 20 pound heavier, 2,600 to 2,800 feet/second

P-47B with 8x0.5 inch versus P-40F with 6x0.5 inch versus P-70 with 4x20mm, conclusion 8x0.5 inch better than 4x20mm, 6x0.5 inch good enough to deliver lethal attack, mainly due to the lower muzzle velocity of the 20mm and having an equal armament weight allowance, one gun out of 4 jamming is worse than 1 out of 6 or 8. Using the results from attacking a ground target the theory says attacking a P-47B from behind by a P-40F would score 12.6, a P-47B 12.39 and a P-70 4.8 hit ratio, 45 degrees off the tail 11.2 to 15.2 to 5.3, 45 degrees from the side 1.49 to 1.72 to 0.86.

See a need for long range bomber escorts anywhere? Development is rarely in a straight line.
 
That is interesting but without digging into the details it looks like somebody was tilting things a little.

How much do you have to "strip" a P-40 to get to equal a P-51?
From the date and Altitudes given I am guessing they meant an Allison powered P-51.
Unfortunately the figures from other tests of the P-40L "Gypsy Rose Lee" model with Merlin engine and the early P-40N-1s don't seem to show quite the same results leaving one to wonder what they took out of the P-40E used in the test?
It is often noted that some of the "stuff" that was pulled out of the P-40N-1s went back in under field conditions. Like the electric starter and bigger battery so they didn't need a couple of men on each plane cranking the inertia starters during a scramble. Also cutting internal fuel to 87 US gallons (72.5imp) to get more speed at just about the time the US was giving the OK to use WEP (about 3 gal a minute for the Allison in the P-40) May give you good speed................over your own airfield.

The Report does give an idea as to the thinking of the time.
The Ballistics of the guns reported on seems a little off. Maybe the higher ups were making decisions based on bad info?
 
The a/c compared was the P-51-NA (NA-91) w/4 20mm cannon - The Basic weight was 200 pounds more than the P-51A. The next question is that of the report source. The Eglin Operational Suitability Test on the P-51-NA stated (Nov 42 Report) that it was clearly superior to P39D and P-40F and (P-38F save ROC) P-47B in speed, ROC, dive - below 18000 feet. Same as P-40 and P-39 in turn, better than P-38 and P-47.

Geoffrey can comment further on the 'lighten the airframe' source.

I would guess that it originated from Wright Field (Oliver Echols approved).

IIRC the West Coast 4th Interceptor Command, ADC Hq put out an impromptu test of XP-51 w/P-39D, P-40E, P-66 and P-38E with much the same results during Dec 1941 - just when Eaker was leaving command of 20th Pursuit Group to take over 8th AF BC under Spaatz. The report was sent to Arnold by General Ryan, commanding, on Jan 4th, 1942 - recommending that AAF take over Mustang Lend Lease

Contrast those two examples to various Wright Field 'lukewarm' opinions.
 
re

I wonder what 20mm cannon they were using for the tests? The 2450 ft/sec is too low for the HS404 derivatives. The 6 seconds of fire at 10 rps would fit for the early 60-round drum magazine feed. However, the 20mm belt-feed was already available by the time the P-47B and P-40F entered service, and the P-38E entered service with 150 rpg belt feed, as did the Mustang Mk IA with 125 rpg belt feed.

The P-70 with 4x 20mm HS404 derivatives used 60-round drums when it entered service with the RAF and USAAF (I think) and at some point was changed over to belt fed .50 cal Brownings (I think) in USAAF service, but the HS404 derivatives M1 and M2 had MVs of ~2850 ft/sec for HE, and ~2950 ft/sec for AP.

Maybe the 20mm they were using in the comparison was a different type, and significantly less capable? Or maybe they did not bother to compare a belt-fed 20mm with the MV of the HS404 derivatives?

This type of thing (along with the idiocies involved in the US attempts to prevent manufacture of the HS404) is what leads to conspiracy theories.
 
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The stripped aircraft reports are from a 6 page message "Report on Fighter Development in the United Sates" sent to Commanding General 8th Air Force dated 22 October 1942, on tests done at Wright Field 5 to 7 October 1942. Signed by Colonel JK Gerhart, it includes a list of aircraft currently in modification centres, which has not made the archives, showing how backlogged they were and noting how different modification requests from different theatres were hurting output.

Then comes the 14 October report for the Director of Military Requirement Army Air Forces from a board consisting of Colonel FH Griswold (Air Defense, Committee President), Colonel JK Gerhart (8th Air Force), Colonel WE Karnes (Air Support), Lt. Colonel Boyd D Wagner (Air Defense), Lt. Colonel MF Summerfelt (Bombardment) and Major CG Peterson (8th Air Force), held at Wright Field and Washington DC 6 to 10 October 1942, which has the praise for the B-17. It comes with the various performance charts.

To end September 1942, the 8th Air Force had done 12 bomber raid days including 2 when the bombers were recalled, 170 sorties attacking, 2 bombers MIA. As far as I know the defending fighters were Bf109 with 1x20mm and 2x7.9mm and Fw190 with 2x20mm high velocity, 2x20mm low velocity and 2x7.9mm. According to Roger Freeman most of the raids had USAAF escorts, then add the RAF ones. Freeman lists 27 B-17 as damaged.

The armament trials "Gun and Cannon Unit, Proof Department, Army Air Forces Proving Ground Command, Elgin Field, Florida", "Comparative Fire Power Tests between 20mm & .50 Caliber Guns", serial 2-42-21, dated 2 August 1942, Signed by Colonel Dudley W Watkins, Chief Proof Department, approved by Colonel Grandison Gardner (though Watkins signs for him), firing tests done 7 to 26 July 1942.

Weapons 0.50 AP-M2, 20mm AP M-75, 37mm M4 M80, 37m M1A7 M74. Expected performance charts include the XP-51B and the "not contemplated" P-40E with R-2600-20.
 
An extraordinarily optimistic assessment. Bitter reality wasn't long in coming.
 
I have no idea what the goal of this test was but the ammunition for all four guns is Armor Piercing ammunition. Which leads to some strange results at times.
The 20mm AP round used a 169-170 gram projectile (with no HE) which explains the low velocity.
Likewise the 37mm M4 gun is using a 750g projectile with no HE vs the standard HE shell that weighed 610g and had 45/48g of HE.
The 37mm AP round had about 400fps less velocity.
The M1A7 37mm gun may have been an designation for the M1 37mm AA gun adapted for aircraft use which was eventually developed into the M9 cannon.
The 37mm M74 AP round was a standard round used in 37mm AT guns and tank guns. The Projectile weighed 870g and had no HE.

Perhaps the goal was to test the guns in an anti-tank (armored vehicle) role, but this ammo had little application against aircraft or even unarmored vehicles (trucks).

The 37mm M1A7 (or M1A2? or T20?) was planned for some of the experimental aircraft like the XP-58 and XP-71 and for one version of the A-26.
listed velocity seems to be the same as AT gun ammo. Some sources claim the AT guns fired HE ammo at slightly lower velocities. They also claim the 37mm AA gun fired the same projectiles as the AT guns and used the same cartridge case but used lower powder charges.
Or somebody flipped a digit and turned 2600fps into 2900fps? The drop distances do not seem to agree with with the velocities.
 
Re. 20mm hits to down a B-17. There does seem to be consensus that the German estimate was around 15 to 20 general hits per kill. That equates to about 2 seconds firing time of the single MG 151/20 Motor cannon in a Bf 109.
Of course, 2 seconds in a firing position behind a B-17 formation was not a happy place to be but, the B-17 losses when unescorted were very bad, which reveals the true vulnerability.
In contrast, the German estimate of required hits for the 30mm MK 108 was 3 hits, about 0,3 sec from a single gun.

Eng
 
The premise of the report is clear, the B-17 really is a Flying Fortress, expect the Germans to at least match this, time to upgrade from 0.50 inch firing solid shot to 37mm or higher, here are their (mostly) solid shot results.

The German estimates of hits to bring down a USAAF heavy bomber were the number required to cause structural failure, fewer rounds were needed if they started a fire, which they often did. As per the USAAF tests on self sealing fuel tanks and the tanks made up a significant part of the airframe area/volume.
 
If I remember well, it was estimated that the average pilot hit about with 2 % of its rounds. This theorically means quite a lot of rounds fired to score thoses 20 hits.
 
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