Late WWII revision to "All-Up-Weight" for specific Lancasters

[JDCAVE]

I have found evidence for a revision to "All-Up-Weight" for specific Lancasters. A memo 19 Jan 1945, (found in AIR 8/333 "Bomber Command Operations, Monthly report to Prime Minister") from A/Cdre Sidney Bufton to Secretary of State for Air [Archibald Sinclair] to be in reply to "Your minute 1 January 1945" that alludes to "…overall results from recent operations suggests Halifax compares well with Lancaster." The author of this note provides a considerable detail and analysis as to why this conclusion is not correct. The author goes on to detail the likely future comparables between the Halifax VI and the Lancaster III/X with the Merlin 224 engines and the likely-to-be-approved increase in the all-up weight of the Lancaster from 65,000 to 68,000 lbs.

I found a Form "B" [AIR 14/3133] for 5-Group, for the raid to Bohlen, March 5/6, 1945 which specifies a different "All Up Weight" for 18 lb boost "Paddle Blade" A/C as 67,000 lbs. All Other aircraft 65,500. This is the first record I have seen for a higher All-up Weight for a non-617 or 9 Squadron a/c (Squadrons that carried "Special Stores"). Note that it doesn't specify whether this would be for RR Merlin or a Packard Merlin 224. Both types could have been Paddle Blade A/C. Note that they WOULD NOT have put Paddle Blade Props on an engine with lower power. The engine would have been "Over Propped" and could have blown up. It's my opinion that the Lancaster X's with Serial numbers KB.774 and above with Paddle Blade A/C would have fit this criteria, however, at no time, did 419 Squadron ORB's record a higher bomb load for those aircraft, right through to the end of hostilities.

But the irrefutable prove that the "All-Up-Weight" exceeded the 65,000 lbs for Mainforce Lancasters (i.e. squadrons other than 617 and 9 Squadrons that had a specified "All-Up-Weight" of 72,000 lbs) can be found in this document where the "All-Up-Weight" is identified as 66,529 on a raid to Leipzig, April 10/4/45, 44 Squadron Rhodesia.

https://ibccdigitalarchive.lincoln.ac.uk/omeka/collections/document/7329

Note that I have not found any other documentation, ORB or otherwise, that identifies the actual All-Up Weight for operations. This does not mean that the actual 14,000 lb limit imposed by limitations of the bomb bay could be exceeded. However, it does provide for a larger load to targets with a deeper penetration.

Jim

 

[JDCAVE]

Further to this, I now understand this form for Bohlen, March 5/6, 1945:

https://ibccdigitalarchive.lincoln.ac.uk/omeka/files/original/408/7246/SChattertonJ159568v10186.2.jpg

"Indicates two bomb loads, one for six aircraft and the other for twelve. Includes H-hour time, preselection and distributor settings,weights, height and false height settings and other notes. On the reverse; aiming instructions, target marking, bombing details, camera settings and other notes."

Jim

 

[emu27]

"Avro Lancaster - The Definitive Record" by Harry Holmes indicates the Lancaster I & III had their gross weight upped to 72,000 as an overload condition in early 1945. Gross weight went from 60,000 to 63,000 in November 1943 and to 65,000 in May 1944.

 

[JDCAVE]

"Avro Lancaster - The Definitive Record" by Harry Holmes indicates the Lancaster I & III had their gross weight upped to 72,000 as an overload condition in early 1945. Gross weight went from 60,000 to 63,000 in November 1943 and to 65,000 in May 1944.

Yes. 72,000 for the BI Special only. my focus above is that it was raised to 67-68,000 lbs for specific aircraft late war. Yes, I have Harry Holmes book, but the ultimate source are the primary historical documents, AIR 8/333 and AIR 14/3133, referenced above.

jim

 

[33k in the air]

For what it's worth, the Aircraft Data Sheet for the Lancaster I/III dated Feb. 2, 1945, lists the maximum take-off weight as 68,000 lbs. (The data sheet for the Halifax VI, with the same date, lists the same maximum take-off weight for that aircraft.)

Some time ago I went through the bomb aimer briefing documents from the site you mentioned in your first posts and compiled the results (I was doing this to ascertain the actual loaded weight of the various SBCs and CPs). Nearly all of the take-off weights were, at most, just a few hundred pounds above 65,000.

The exceptions were:

Jan. 2, 1945 — one aircraft had a 67,064 lbs take-off weight (1 x 4,000-lb and 14 SBCs of 150 x 4-lb; fuel load, 1,700 gallons)
Feb, 7, 1945 — one aircraft had a 66,466 lbs take-off weight (14 x 1,000-lb; fuel load, 1,450 gallons)
Feb. 8, 1945 (vs. Politz) — one aircraft had a 66,869 lbs take-off weight (1 x 4,000-lb and 12 x 500-lb bombs; fuel load, 2,154 gallons)
Feb. 13, 1945 (vs. Dresden) — one aircraft had a 66,677 lbs take-off weight (1 x 4,000-lb and 12 No. 14 CPs; fuel load, 2,154 gallons)


ETA: The TARE weight from the forms show 41,650 lbs for H2S-equipped Lancasters and 41,100 lbs for non-radar-equipped aircraft (thus implying the H2S installation added 550 lbs). Interestingly, the TARE weight is 41,200 lbs for the Lancasters which flew with 66,000+ lbs take-off weight.

 

[JDCAVE]

Very good 33K. That sheet escaped my search on this. Very useful and confirms Bufton's memo on the subject, 19 Jan 1945.

Jim

 

[33k in the air]

(I was doing this to ascertain the actual loaded weight of the various SBCs and CPs).

For anyone wondering about the results of that, these are the weights most commonly derived:

676 lbs = SBC of 150 x 4-lb incendiaries
476 lbs = SBC of 16 x 30-lb incendiaries
376 lbs = SBC of 12 x 30-lb incendiaries
266 lbs = SBC of 8 x 30-lb incendiaries

484 lbs = No. 14 Cluster Projectile (106 x 4-lb incendiaries)

Explosive bombs were more varied; sometimes the class weight was used, other times various actual weights. Some examples of derived actual weights:

4,160 lbs = 4,000-lb HC
1,059 lbs = 1,000-lb MC
1,065 lbs = 1,000-lb AN-M65 U.S GP
1,042 lbs = 1,000-lb AN-M59 U.S. SAP

The weight of a packet of Window can also be calculated.

460 lbs = 23 packets (1 packet would be 20 lbs)
682 lbs = 31 packets (1 packet would be 22 lbs)

 

[JDCAVE]

snip....

The weight of a packet of Window can also be calculated.

460 lbs = 23 packets (1 packet would be 20 lbs)
682 lbs = 31 packets (1 packet would be 22 lbs)

The weight of the Mk 14 cluster matches my understanding. I believe the number of IB's in the SBC's varied a bit. Dad's logbook gives the number of SBC's but not the number of IB's. the ORB gives the number of IB's so I can calculate the number of IB's in each container in those instances.

I'm interested in your window calculation. How many "bundles" in a packet? For some operations we know the rate of "windowing." Dad mentioned that for Dresden "...It was a very long trip and the amount of "window" we had to put in was absolutely disturbing. It stretched all the way from the mid upper turret, along the walls of the fuselage, all the way from the mid upper turret, right forward to the nose of the aircraft, and it was piled up about 5 or six boxes high. And that took us about an hour and a half with all seven members of the crew, working like [hell] to get the stuff properly arranged and stacked. It came in a great big truck I remember and it was one hell of a job."

...So it was the job of the aircrew, not ground crew to load the window into the aircraft. I don't know how accurate dad's recollection was of this, but I note that the above "all-up-weight" calculations by 44 Squadron doesn't seem to factor in the weight of the window, which would seem to vary by operation.

Jim

 

[33k in the air]

The weight of the Mk 14 cluster matches my understanding. I believe the number of IB's in the SBC's varied a bit. Dad's logbook gives the number of SBC's but not the number of IB's. the ORB gives the number of IB's so I can calculate the number of IB's in each container in those instances.

In regards to SBCs, this is what I've found:

The main one used earlier on held 90 x 4-lb, although sometimes it was only filled to 2/3rds capacity, or 60 x 4-lb. It could alternatively hold 8 x 30-lb. (Non-incendiary loads for this size of SBC were 6 or 8 x 40-lb GP bombs, or 12 x 20-lb fragmentation bombs.)

A larger version was introduced later which held 150 x 4-lb, although, according to the ORBs for 106 Squadron, this too was sometimes filled to only 2/3rds capacity, or 100 x 4-lb. This same container could hold 12 x 30-lb, and possibly 16 x 30-lb (I'm not certain references to 16 x 30-lb loads are this same SBC or a different model, althouhh I'd guess it is the same). I don't if it could contain non-incendiary bomb combinations

There was also evidently a smaller SBC developed for the Hudson, which held 40 x 4-lb incendiaries.

I've come across very little technical data about SBCs online. While the British ordnance manuals from the period that are available give specifications about bombs and cluster projectiles, the small bomb containers are never covered. I've had to piece things together from what sources I could find.


In regards to the No 14 CP, the total weight, according to British ordnance manuals, was 450 lbs. That's 34 lbs lighter than the weight derived from the 44 Squadron load weights. I don't know the reason for the discrepancy; it may be the ordnance manual misstated the full weight (the total weight of the No. 16 CP is definitely wrong, as it is less than the nominal weight of the bomblets carried), or it may be the weight of the bomb carriers needed in the bomb bay, or it might be some other reason.

I'm interested in your window calculation. How many "bundles" in a packet? For some operations we know the rate of "windowing."

The weight of Window carried is listed on some of the 44 Squadron weight tables found at the IBCC site. Here's an example. Here's another example.

It's been awhile since I did it, but as I recall I just jotted down out of mild interest the figures from one of the bomb aimer briefing documents; or maybe I crosschecked the Window amount against an available weight table file for that mission; I can't remember. I did not record which specific document i got it the figures from, unfortunately. Packet and bundle may be interchangeable.

I went through some of the weight tables and bomb aimer briefings seeing if I could find it again, but and didn't come across the specific numbers I mentioned, but there are a fair number of files to go through..

 

[JDCAVE]

33K: I don't think package and bundle would be the same thing. The Form "B" for Cologne, March 2, 1945 calls for windowing at "Rate G" at 10 minutes before target and to the back to the battle line, and the briefing document indicates "5 bundles per minute" 10 minutes before target and to the battle line. so I don't think they'd be dropping 5 X 22 lbs of window every minute. I suspect that your "packages" contained "bundles of window, that I think were maybe an inch thick. I shall look around in the early stuff I have on window to see if I can get more specifics. Windowing rates aren't always in the briefing document. They often did a lot of windowing over the target to saturate the radar predicted flak. The Lancaster had the "Cheese Grater" window shoot on the starboard side of the aircraft just aft of the bomb aimers station.

That second example of Window weights for 24-4-1944, would match up with a 5-Group raid to Munich, a deep penetration and consistent with a full load of petrol. It definitely gives us an indication of the weight of window carried on a deep-penetration raid. At the time, France would have been occupied and defended by the Nachtjagd, so they would have windowed from the French coast and all the way to target and back (I speculate).

I've attached specs I have for the Mk 14 and Mk 17 Cluster projectile. Dad carried the Mk 17 on a couple of occasions.

Note: removed Mk 17 cluster image.

 

[33k in the air]

33K: I don't think package and bundle would be the same thing.

Perhaps so. I wish I had written down exactly which file provided the Window figures I mentioned, so it could be looked at more carefully.

I've attached specs I have for the Mk 14 and Mk 17 Cluster projectile. Dad carried the Mk 17 on a couple of occasions.

View attachment 656061

There was also the U.S. AN-M17 aimable cluster, which held 110 x 4-lb incendiaries, which was carried by Bomber Command on numerous occasions. In some ORBs it is referred to as the M17. But I wonder, due to the number 17 being used for both, if references to a No. 17 cluster actually means the U.S. aimable cluster. On its face it seems odd for a heavy bomber to be carrying 20-lb fragmentation bombs.

For example, 408 Squadron ORBs list 2 x 1,000 MC and 11 x No. 17 clusters being carried on a mission to Mannheim conducted on Mar. 1, 1945, except for one aircraft which carried 12 x No. 14 CP instead. It seems strange why all but one of the bombers would be carrying 20-lb frag bombs, so I can't but help but wonder if No. 17 in this instance really means the u.S. M17 cluster, especially considering both carry nearly identical numbers of 4-lb incendiaries.

(This is the only 408 Squadron mission on which a No. 17 cluster is listed as a bomb load item.)


As an aside, if anyone is looking for ordnance manuals, the website Bullet Picker has quite a selection of WW2 and later official military ordnance manuals available for download in its Library section.

 

[JDCAVE]

That's a mistake on my part. I don't think that clusters with fragmentation bombs were ever carried on any 419 Squadron raids.

Jim

 

[JDCAVE]

33k: I hadn't looked at your post #9 as closely as I should have earlier. Those window weights are useful. The second link corresponds to an op to Berlin, March 24/25, 1944, with the maximum fuel load of 2154 gallons. 600 lbs of window were carried. Late war deep penetration raids to Dresden, Chemnitz, etc, may have had shorter routes over enemy territory, with the allies occupying more eastward territory. Still I calculate that at least 400 lbs were dropped, and given the requirement for a margin of error, they probably carried at least 500 lbs, with 600 lbs possibly being the upper limit of window carried.

No. 1-Group Operation Instruction No. 13 (Revised 15th of March, 1944), Appendix "A" Window dropping areas.

Concerning window, the Instruction states:

"This countermeasure is effective in preventing the efficient operation of C.G.I. control of enemy night fighters and confuses to a certain extent the A.I. carried in night fighters. It also prevents the effective operation of the Wurzburg (G.L.) apparatus used in the control of flak and searchlights....[snip]

"The following letters are to be used to denote the rates of discharge indicated:

Rate A - 1 Bundle per 2 minutes.
Rate B - 1 Bundle per 1.5 minutes.
Rate C - 1 Bundle per 1 minute.
Rate D - 2 Bundles per 1 minute.
Rate E - 3 Bundles per 1 minute.
Rate F - 4 Bundles per 1 minute.
Rate G - 5 Bundles per 1 minute.

"WINDOW is to be discharged in the two areas as follows:-

Area I: Rate D within 20 miles of the target only.
Area II: (i) Throughout the route to and from the target at Rate C
(ii) Within 30 miles of the target Rate D with the exception of BERLIN when Rate D will commence 50 miles from the target.

This is useful to me at least as I have seen Rate G referred to for dad's operation to Cologne (March 2, 1945). Window was to be dropped at "Rate G" beginning 10 miles before the target and through the defended area. This rate (5 bundles/minute) was also used on the op to Essen, March 11, 1945, "from bomb-line to bomb-line."

Jim

 

[33k in the air]

For anyone wondering about the results of that, these are the weights most commonly derived:

676 lbs = SBC of 150 x 4-lb incendiaries
476 lbs = SBC of 16 x 30-lb incendiaries
376 lbs = SBC of 12 x 30-lb incendiaries
266 lbs = SBC of 8 x 30-lb incendiaries

484 lbs = No. 14 Cluster Projectile (106 x 4-lb incendiaries)

From the above, incidentally, one can calculate the approximate empty weight of the SBC or Cluster Projectile (that is, without specifically the bombs):

76 lbs for the 150 x 4-lb and 16/12 x 30-lb
66 lbs for the 8 x 30-lb
60 lbs for the 106 x 4-lb