Results 1 to 6 of 6

Thread: 'AVBS' testing: A bomb sight?

  1. #1
    Join Date
    Nov 2007
    Location
    Vancouver Island, British Columbia, Canada
    Posts
    1,016
    Thanks
    1
    Thanked 10 Times in 10 Posts

    Default 'AVBS' testing: A bomb sight?

    According to a logbook, 59 Squadron, Coastal Command, tested 'AVBS' on a Liberator and a Fortress at Thorney Island in December 1942.

    Assume 'BS' stands for bomb sight.

    Does anyone have more info on the equipment?

    Robert
    Last edited by robstitt; 5th February 2020 at 18:34. Reason: Typo

  2. #2
    Join Date
    Apr 2017
    Location
    Canberra
    Posts
    128
    Thanks
    8
    Thanked 15 Times in 14 Posts

    Default

    AVBS:
    Haven't come across this before, however a quick check finds
    "The Low Level Bomb Sight Mark III - Angular Velocity"
    so described.

    And continues:
    "The last named was unique in that a new approach to bomb sighting problems-
    that of angular velocity which was much less critical to height errors than other
    orthodox sighting systems...devised particularly for attacking submarines"

    Source: Armament Vol I Bombs And Bombing Equipment SD 719 (Air Ministry AHB 1952) (p 273)
    (MLRS facsimile edn)

    There's an extensive illustrated description at pp288-292 a bit too much for me to reproduce here, however, this gem from p291
    "The Mark III sight was introduced for service trials in late 1942...on 22 Dec 1942 the sight was officially introduced into the service...to be known as LLBS Mark III" (sic! see below)

    As the log entry above refers, "AVBS" tested by 59 Squadron Coastal Command Dec 42 matches the dates, and better, matches Service Trials summary below (having wheedled ABBYY OCR into co-operating with dull brain and fingers to record this fuller extract)

    "The Mark III sight was introduced for service trials in late 1942. The report on the trials contained the following recommendation :
    ' For normal operational requirements it is considered that A.V.B.S. (Angular Velocity Bombsight) is by far the most efficient low level bombsight available for Coastal Command, and also low level daylight bombing on small targets, for the following reasons :
    (a) It is simple in use and sighting.
    (b) No height setting is required for accurate stick bombing ; thus, only one adjustment, namely, approximate ground speed, is required on the computor box.
    (c) Accurate bombing may be done in a climb or a dive, or following evasive action.
    (d) Late sighting is no deterrent.'

    On 22 December 1942 the sight was officially introduced into the service, and at the end of the month A.C.A.S.(T) stated an immediate minimum requirement of a hundred of these sights to be known as L.L.B.S. Mark III. The sight itself once again consisted of two units, computor box and sighting head, but this time gyro stabilised in pitch. The method of depicting the moment of release was novel and worthy of mention; it was done by presenting a graticule which appeared to the bomb-aimer as an illuminated step ladder. This ladder moved down the graticule plate in accordance with the ground speed set on the computor box chart, thus when referred to a datum point on the terrain below, the aircraft, was in fact a measure of the angular velocity.

    The normal datum point was, of course, the target which ' moved ' down the overtaking ladder, getting faster and faster as its range decreased until that vital moment when the speed of ladder and target were the same, and in reference to the moving ladder, the target was motionless. This was the correct moment at which to release the bomb. Apart from a few minor modifications which became necessary on fitment to various types of aircraft, the Mark III soon became a standard item of bombing equipment for aircraft during the Second World War which employed this type of attack. "
    Source: as above, pp291, 292

    Despite the unfortunate death of David Westwood in 2016, MLRS continues to provide facsimiles of rare and useful documents, if now only by download (as his wife
    explains https://www.mlrsbooks.co.uk/about_mlrs). He was a good bloke, once replacing a large order of mine (print!) that went missing in the post...by CD, then, I fancy.

    Please excuse the repeated/extended edits of this post. Poor prep on my part, now perhaps coherent.


    Amended
    After several attempts to add images of the Sight units and the graticule image, thanks to earlier help, ultimately succeeded:

    AVBS ie LLBS MK III set
    www.211squadron.org/LLBS_AV_Mk_III_post_1.jpg


    Graticule image
    www.211squadron.org/LLBS_AV_Mk_III_post_2.jpg

    Source: Armament Vol I as previously cited


    Again, my apologies for numerous tedious edits
    Don Clark
    www.211squadron.org
    Last edited by Don Clark; 6th February 2020 at 04:40. Reason: addnl

  3. #3
    Join Date
    Nov 2007
    Location
    Vancouver Island, British Columbia, Canada
    Posts
    1,016
    Thanks
    1
    Thanked 10 Times in 10 Posts

    Default

    Thanks for the excellent feedback, Don.

    For the record, the logbook states that the crew tested the AVBS on the 7th December 1942 in Liberator FL916 'P' with W/C Wright and a Mr Richards - this would have been just before the squadron relinquished its Liberators for Fortresses - with an additional practice run on December 22 in Fortress FK202 'B', a night test of the AVBS with W/C Bartlett [the squadron CO].

    Source: Logbook for Hervey R LONGMUIR, navigator, 59 Sqn, courtesy Lorenzo del Mann, grandson.

    As far as I know, the AVBS was never used in encounters with U-boats, the depth charge release point being judged by the captain by eye.

    A quote from a Fortress flight engineer: 'Time was of the essence and the aircraft would normally go straight into the attack… so it would be tracking over the target long before the navigator could get into position to use the low-level bombsight. The normal way to drop the depth charges was for the pilot to aim by eye… this was practised using dummy targets at between 50 to 150 feet.'

    Robert
    Last edited by robstitt; 6th February 2020 at 05:19. Reason: Typo

  4. #4
    Join Date
    Nov 2007
    Location
    Vancouver Island, British Columbia, Canada
    Posts
    1,016
    Thanks
    1
    Thanked 10 Times in 10 Posts

    Default

    Additional note: Longmuir and Bartlett went to H.Q.C.C. on the December 16, 1942, to deliver the results of the AVBS tests.

    Robert

  5. #5
    Join Date
    Nov 2007
    Location
    Vancouver Island, British Columbia, Canada
    Posts
    1,016
    Thanks
    1
    Thanked 10 Times in 10 Posts

    Default

    Don,

    Could you please contact me via my email address, accessible by clicking on my user name 'robstitt'.

    Thanks.

    Robert

  6. #6
    Join Date
    Apr 2017
    Location
    Canberra
    Posts
    128
    Thanks
    8
    Thanked 15 Times in 14 Posts

    Default

    Thanks Robert.

    For general information, like the Campbell thread, here I illustrated by loading/linking images which I loaded to my own
    site, simplest for me.

    The AHB monograph I cited, although once a Secret Document splendid in pink cloth boards, is quite readily available in relevant archives and in facsimile PDF by download from MLRS Books.
    See https://www.mlrsbooks.co.uk/bookstor...t/item973.html

    Anyone also wishing to reference same (eg, AVBS notes) might best cite the original work title
    ie
    Armament Vol I Bombs And Bombing Equipment SD 719 (Air Ministry AHB 1952, MLRS facsimile edn)

    As for the images, I'd like to take them down in a week or so, if that's OK.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •