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bubble_head
Austin, TX, USA
New User
E-2 Private


Posts: 25

Need help from a Desert Rat!
Posted on: 4/28/2017 11:34:04 PM
Hey cats!

FNG here. Former US Navy Submariner. I was a twidget (An ET-COMM.) But, As a lover of military history and one of my favorite areas being tanks warfare and especially WWII, I am currently reading a book called "Killing Rommel" by the great Steven Pressfield.

There is a passage in it I need clarification with. I was hooping somebody familiar with Desert warfare might know.

Here is the passage. To set it up and give some context, the group of Brit LRDG (Long Range Desert Group..basically what us Yanks would call 'Lerps' I guess) are heading across the North African desert in an assault vehicle, doing some recon. Here is the quote..........

"The air beating past our brows is pellucid. Adam himself breathed nothing purer. Were it noon, we'd be squinting across the surface of a mirage lake, with heat shimmer rising fifty feet into the air. But our trucks can't travel at noon; the shadow is too short to give a bearing on the sun compass."

So....why would they need to use a sun compass and not just a regular compass? I know they didn't have GPS back in WWII, but did they really have nothing more techno than a sun compass?

thanks in advance for your time!

Cheers, mates.

SJ
Belfast N Ireland, UK
top 10
E-9 Sergeant Major
Posts: 697

Re: Need help from a Desert Rat!
Posted on: 4/29/2017 4:26:16 AM
Not quite a Desert Rat old boy - but the son of one, and got my knees brown east of Aden when a lot of that region was pink on a world map.

Your question reminded me of hosting a party of Yanks(some crap hat armoured unit) we hooked up with, whose unit designation had so many digits I mistook it for a telephone number.

The party visited us on a posting to Bahrain. A wild lonely and desolate spot. The New Yorkers must have felt right at home.

We took them on their first desert patrol- and introduced them to the Coles Mk2 sun compass. They fiddled with it, lost one of 'my precious' spare gnomon clips, and breezily announced that as a modern army they had decent Swiss magnetic compass and didn't need relics like this....

We gave them a simple NAVEX and shouted "Your doomed" (aka Pte Fraser) as they drove off on the wrong side of the dirt track.

Time past- around midday we got a signal "Hummm we seem to be temporary lost" . It was midday -and as we were neither dogs or a Guards Regiment we had some char and waited for the 'cool of the day'

We then placed a magnetic compass on the Rover, and noted how many degrees ALL THE BLOODY METAL had defected the needle. Set a bearing on the Coles and recovered our guests.

As I side note, I am old enough to have had a drink with the inventor of the Sun Compass. Old Indian Army gent who was Member of Parliament for Hemel Hampstead and "Father" of the House. James Allason, and if you own your own home in England, its thanks to him. His simple sun compass was used by the LRDG and most Allied units until replaced by the Howard and the more complicated Coles.

George
Centre Hastings, ON, Canada
top 5
E-9 Cmd Sgt Major
Posts: 5313

Re: Need help from a Desert Rat!
Posted on: 4/29/2017 6:29:04 AM
SJ, is this it?



I am tempted to ask how you use it. Would I understand? Are there tables that go along with it, tables that would tell you the position of the sun in the sky on any given day in the year? There must be several variables that the operator would have to account for

Also welcome to bubble___head. This is what I like about this forum. You come on board and immediately give us something intriguing.

While I was trying to find information on this Sun Compass, I saw a reference to a US Army Sun Compass manufactured by Abrams in Lansing, Michigan during WW2 so I guess that your guys needed them too.

[Read More]

Cheers,

George

SJ
Belfast N Ireland, UK
top 10
E-9 Sergeant Major
Posts: 697

Re: Need help from a Desert Rat!
Posted on: 4/29/2017 8:13:36 AM
Yes George, that's the Coles. Right, I will give a quick explanation as to how to use "the instrument". Any questions at the end, raise your hand and I will nominate...

1. The "instrument" can be used over a Lat of 40S to 40N. The bearing plate illustrated appears to be engraved for use in the Middle East.

2. The only data or "tables" required is; (i)Lat and Long of the location (say Baghdad 33.32N, 44.36 E, as any self respecting Cruise Missile will tell you)(ii )the date, and (iii) either GMT or LMT from which LAT (local true time) can be calculated. Thus the daily change in the sun's bearing can be allowed for in moving the gnomon up or down the date scale (that's in the bottom segment of the instrument).

3. You will observe a series of semi-ellipses intersected by curves are inscribed on the upper part of the bearing plate- they are marked 6,12,18,24, 30,36, 40. - these denote latitude- the curves that bisect them indicate time. The time is shown in hours above the 40 latitude ellipse. Its not clear from the illustration, but the upper figures are in red and for S of Equator and the lower figures in black for north. The hours are sub divided into quarters, and the shadow pointer can be set at any intersection of latitude and time.

4. On the bottom of plate - either side of the gnomon slide slot, you can just make out the months of the year. each divided into periods of 10 days. Jan- June upwards on Right, July- Dec downwards on the Left. The horizontal line on the gnomon slide can be thus set to the date.

5.The illustration shows only one gnomon rod fitted to the three armed wing nut, the other positions are in the triangular index piece (TIP) and the 180 mark at the bottom of the plate.

To use - set TIP to the direction of vehicle travel (MT Section will have zeroed the instrument with a spirit level and used a prismatic compass (at least 20 meter clear if heavy AFV) for a true bearing. Sight along two gnomons and align with fixed point,
set the gnomon slide to today's date, and shadow guide to intersection of latitude/time.
Turn the bearing plate until the sun's shadow lies true along the edge of the shadow,
Final Check on the scribed mark on G slide is at correct date- and secure the three armed nut.

Now turn the bearing plate until the required course is opposite the TIP - clamp the plate in position, start engine, and follow the bearing as you would a conventional compass. At all times drive the vehicle keeping the centre line of the shadow of the gnomon dead on the radial edge of the shadow guide- This position is called the Shadow on Time. Like all good nav, you pick up a mark in direction of travel and head towards it.

But, remember to shift the shadow guide with 15 minute settings.

The simpler Howard compass uses the Davis Azimuth Tables gives a mean equation of time for calculating LAT. If have the Azimuth, you pencil in the correct radii for the times of the day. Then its Index on course and Shadow on time.

Now....darkness falls, the sun sets, and horrible things come out to play..How do you use a Coles at night???



George
Centre Hastings, ON, Canada
top 5
E-9 Cmd Sgt Major
Posts: 5313

Re: Need help from a Desert Rat!
Posted on: 4/29/2017 11:23:04 AM
OK, SJ. Wow. I have a feeling that I would be the driver or a sleeping passenger while someone sharper figured out where we were going.

I've done a little orienteering with a magnetic compass so I understand how to take bearings and to calculate back bearings but this device seems more complex.

The device is really very clever as you explain it.

Is it only designed for work between the 40's just because to make it useful anywhere else would require a much bigger plate?

It would not be of much use in the extreme latitudes at certain times of the year when the sun is low on the horizon or doesn't appear at all.

Cheers,

George

SJ
Belfast N Ireland, UK
top 10
E-9 Sergeant Major
Posts: 697

Re: Need help from a Desert Rat!
Posted on: 4/29/2017 12:22:31 PM

Quote:
OK, SJ. Wow. I have a feeling that I would be the driver or a sleeping passenger while someone sharper figured out where we were going.

I've done a little orienteering with a magnetic compass so I understand how to take bearings and to calculate back bearings but this device seems more complex.

The device is really very clever as you explain it.

Is it only designed for work between the 40's just because to make it useful anywhere else would require a much bigger plate?

It would not be of much use in the extreme latitudes at certain times of the year when the sun is low on the horizon or doesn't appear at all.

Cheers,

George
--George


The blog on this thread is not the best medium to explain this instrument. And I am trying to recall drills and lesson plans from the 70s! Amazingly the Coles Mk2 and 3 were still part of the Royal Irish Hussar kit in the 1991 Gulf War.

And yes - north and south of the 40s you tended to get too weak a shadow. On Suffield, Alberta (what about 50 North?) it wouldn't work. Canadians seem pretty good at looking at the sun in the sky and telling you both time and bearing !

Also, as related in the original question, the midday high angle can negate shadow.

George
Centre Hastings, ON, Canada
top 5
E-9 Cmd Sgt Major
Posts: 5313

Re: Need help from a Desert Rat!
Posted on: 4/29/2017 3:12:10 PM
CFB Suffield is a tad north of 50. Pretty big place as you would know better than I, SJ.

2700 sq. km.

Does the British Army Training Unit still operate out of Suffield?

I know that the Brits were looking for a place to train armoured units and live fire artillery and they lost their bases in the Middle East.

Nothing suitable at home so they signed a deal with Canada after the war.

Suffield has lots of space for the type of training that the British wanted to do.

The British were there for a long time. They may still be.

Cheers,

George

Bubble_head
Austin, TX, USA
New User
E-2 Private


Posts: 25

Re: Need help from a Desert Rat!
Posted on: 4/29/2017 6:33:34 PM
Ah, the bloody metal! That explains why the sun compass. Thank you sir. I enjoyed your post. You're a fine writer! @ crap hat unit!

I understand how tricky the sun compasses can be. After reading your post and my aforementioned book. It said that one degree off will put you three miles away from your target on a 100 mile trip. And of course they had to be tweaked dverh couple hours to account for the sun's movement across the sky.

Thanks again.

Bubble_head
Austin, TX, USA
New User
E-2 Private


Posts: 25

Re: Need help from a Desert Rat!
Posted on: 4/29/2017 6:42:27 PM
Good Lord! That's way more complex than I pictured it after reading about it in the book! Pressfield described it as a brass disk that laid horizontally mounted above the dash between the driver and the passenger seat, about three inches diameter, with a needle sticking up vertically from it's center. And that you just rotate the disc do as to align the needle shadow with your desired direction. So I was imagining a simple, N, S, E, W sort of setup.

Apparently not so. Also interesting in the book was descriptions of the incredible difficulty in driving across sand dunes. A sudden jerk of the wheel or acceleration and you can sink to your axles! They described the sand as testing like silk! And having to dig themselves out about a dozen times a day....in 130 degree heat. Whew.

SJ
Belfast N Ireland, UK
top 10
E-9 Sergeant Major
Posts: 697

Re: Need help from a Desert Rat!
Posted on: 4/30/2017 2:06:10 AM

Quote:
Ah, the bloody metal! That explains why the sun compass. Thank you sir. I enjoyed your post. You're a fine writer! @ crap hat unit!

I understand how tricky the sun compasses can be. After reading your post and my aforementioned book. It said that one degree off will put you three miles away from your target on a 100 mile trip. And of course they had to be tweaked dverh couple hours to account for the sun's movement across the sky.

Thanks again.
--Bubble_head


You are welcome sir. The description fits the early Allason sun compass. Never used one, but it inspired the Howard.

Crap hats. I am afraid the quality and attitude/aptitude of US military in the 1970s left a lot to be desired. It took a while to shake off the Vietnam demons. Servicemen seemed to lack that sense of unit pride - that essential esprit de corps- that creates the bond and something to live up to. So they acted up and know all. When I was in Berlin, I recall historians being brought in to instil a sense of American martial history, whereas- in that era, even a lowly English/Scottish/Irish/Welch line regiment had their own unique heritage, often back to the 1690s and beyond.

I know the amalgamations make fiscal sense - but the British Army struggles to retain that unique and precious sense of unit tradition. That powerful evocative first person plural that is timeless. "Gentlemen..we the 27th did not fold at Waterloo and we are not going to let the absence of transport cause us to fold now...get the men on their feet and remind them of who we are!" etc.

George asks about Suffield. I saw a defence review paper in 2015, and there still is a cadre maintaining the site- so I presume the Brits are still there. Salisbury Plain gets a bit cramped for modern mechanised warfare.

Nobody interested in how to use a Coles sun compass at night? Take one tin of paint (luminous).....Seriously, the instrument can be used at night! I kid you not.

George
Centre Hastings, ON, Canada
top 5
E-9 Cmd Sgt Major
Posts: 5313

Re: Need help from a Desert Rat!
Posted on: 4/30/2017 6:37:34 AM
I am SJ. Intriguing.

I have been cheating and found a reference to an American designed Abrams sun compass that could be used at night because it had a glass tipped stylus that was filled with an illuminating substance. But there was no explanation of how that magnified whatever light source created the shadow.

So what did you guys do with the paint?


I found this picture. Does the driver keep one eye on the sun compass while he drives or does he take a reading and then look ahead, drive to a point that he picked out in the distance and then reset the sun compass?

[Read More]


Long Range Desert Group in North Africa

I couldn't see the sun compass but this has to be a cool photo. It was too big to put in as an image so just hit the READ MORE

[Read More]

Is that a Lewis gun? Minus the cooling element?


Cheers,

George

SJ
Belfast N Ireland, UK
top 10
E-9 Sergeant Major
Posts: 697

Re: Need help from a Desert Rat!
Posted on: 4/30/2017 8:09:38 AM

Quote:
I am SJ. Intriguing.

I have been cheating and found a reference to an American designed Abrams sun compass that could be used at night because it had a glass tipped stylus that was filled with an illuminating substance. But there was no explanation of how that magnified whatever light source created the shadow.

So what did you guys do with the paint?

Quote:


Apologies George- a wee bit of Royal Irish blarney- Night nav with the Coles Sun compass was first used by the three wise men.

1. Insert the second gnomon at 180. Set the required course to the index, and turn the vehicle until the two gnomons are aligned on ....wait for it....Polaris. Which is never more that 2 degrees on True North. Indeed if your route is north, abandon the compass and just "follow the bloody star". Hope I am not losing you with all this science.


Quote:


I found this picture. Does the driver keep one eye on the sun compass while he drives or does he take a reading and then look ahead, drive to a point that he picked out in the distance and then reset the sun compass?

[Read More]


Quote:


The latter


Quote:



Long Range Desert Group in North Africa

I couldn't see the sun compass but this has to be a cool photo. It was too big to put in as an image so just hit the READ MORE

[Read More]

Is that a Lewis gun? Minus the cooling element?



First I think the unit in question is more likely to be SAS. Will check images.

Secondly, the LMG in question is the Vickers K class- a weapon usually associated with RAF bomber turret mounts . My late father used to relate tales of fellow Ulsterman Robert Mayne 'borrowing' any Vickers K that was not nailed down - to arm his jeeps.

George
Centre Hastings, ON, Canada
top 5
E-9 Cmd Sgt Major
Posts: 5313

Re: Need help from a Desert Rat!
Posted on: 4/30/2017 12:00:52 PM
SJ what of the device that I mentioned that had an illuminated stylus and could be used at night. I don't understand how that works.


Cheers,

George

SJ
Belfast N Ireland, UK
top 10
E-9 Sergeant Major
Posts: 697

Re: Need help from a Desert Rat!
Posted on: 4/30/2017 12:04:18 PM

Quote:
SJ what of the device that I mentioned that had an illuminated stylus and could be used at night. I don't understand how that works.


Cheers,

George
--George


I can only speculate that the illuminated stylus is to help align with Polaris. Like all "experts", in truth, I know a great deal about very little- to wit, the sun compass types used by the British Army. An illuminated stylus would make sense.

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