[ARC5] US Submarine ELINT WWII, (was British ZB......?)

Thu Apr 8 05:07:56 EDT 2021

Al:

     Thanks for your note and reminder of your earlier poster on the subject.  I also found this reference https://tinyurl.com/3f79nt32 that provides more detail of the fuzing mechanisms used on both weapons.  (Before reading this reference I had thought that these weapons just hit the ground and went off like other iron balms (deliberate misspelling.))  

All:

     A while back I calculated the velocity of Little Boy when it detonated at 1850  FAGL.  Reading somewhere that the weapon was released at 31,000 feet, it would have fallen 31000 – 1850 feet or 29,150 feet.  Using D = 1/2gt^2, then t = SQRT(2D/g) = SQRT(2*29150/32) = ca 43 sec of freefall.   Then, V at 43 sec = g*t or 32*43 = 1,376 fps or 1376 * 3600 / 5280 = 938 mph, i.e., supersonic.  (I assumed that the 5 tons of weight of the weapon overcame any air resistance.)  The 43 seconds of fall corresponds roughly to what I’ve also heard from Tippet’s and other crew reports.

73 de

Gene Smar  AD3F

From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On Behalf Of Al Klase
Sent: Thursday, April 08, 2021 12:21 AM
To: arc5 at mailman.qth.net
Subject: Re: [ARC5] US Submarine ELINT WWII, (was British ZB......?)

Gang,

I recalled that I did a poster on this  <http://www.ar88.net/stuff/FUZING%20THE%20BOMB.pdf> for the 75th anniversary back in 2015.  Out Museum is located at Camp Evans which was the home of Army Radar.

Al

On 4/8/2021 12:01 AM, Al Klase wrote:

Gene,

Actually, that antenna was a standard part of the APS-13, one on each side of the aircraft tail.

The weird part is that the bombs carried 4 APS-13's each,  They actuated relays that were wired in series parallel to ensure detonation near 2000 feet, but prevent premature detonation.  So at least two radars had to vote to explode the bomb.

Al

On 4/7/2021 7:30 PM, Gene Smar via ARC5 wrote:

Speaking of Japan and RADARs, I’ve always thought it ironic that the APS-13 “Archie” tail warning RADAR was mated with the Yagi-Uda antenna as part of the altimeter fuze for both Little Boy and Fat Man.  

C’est la guerre.

73 de

Gene Smar  AD3F

From: arc5-bounces at mailman.qth.net <mailto:arc5-bounces at mailman.qth.net>  [mailto:arc5-bounces at mailman.qth.net] On Behalf Of Tim
Sent: Wednesday, April 07, 2021 6:12 PM
To: Hubert Miller  <mailto:Kargo_cult at msn.com> <Kargo_cult at msn.com>
Cc: To: ARC-5  <mailto:arc5 at mailman.qth.net> <arc5 at mailman.qth.net>
Subject: [ARC5] US Submarine ELINT WWII, (was British ZB......?)

Hue said: But by US standards Japanese radars were rudimentary, not widely deployed, and also ( without referring to my docs ) I believe mostly operated on lower frequency bands than US. It just seems rather less likely or certainly, uncommon 

[snip]

--------------------------------

Generally true.....US Subs used the AN/APR-1 (and -4 presumably) hunting IJN ships/submarines in the Pacific in WWII.  ..In researching the AN/APR-1 that I am playing with I learned that the USS Batfish sank an IJN submarine after the APR-1 detected its 150 mc radar. Those IJN subs also carried 3 Gc radars, at least late-war.  The APR-1 (SPR-1) could detect both radar band emissions. I would expect many other intercepts were made with this gear.  It was a good passive system and the APR-4 variant was used well into the Vietnam war era aboard EB-66 aircraft, probably others.

Some details if you're bored:  http://www.n6cc.com/an-apr-1-apr-4-radar-comm-surveillance-receiver/

Tim

N6CC

______________________________________________________________
ARC5 mailing list
Home: http://mailman.qth.net/mailman/listinfo/arc5
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:ARC5 at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: https://www.qsl.net/donate.html

-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net

______________________________________________________________
ARC5 mailing list
Home: http://mailman.qth.net/mailman/listinfo/arc5
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:ARC5 at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: https://www.qsl.net/donate.html

-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/arc5/attachments/20210408/4e0fe539/attachment-0001.html>