Interpreting a trench map

[BearsdenWarMem]

Good morning, Please can I get some advice on interpreting a map I found in the war diary of the 9th HLI?  The area is in front of the Hindenburg Line, south-east of Arras on 20th May 1917.  My questions are

(1) how to interpret the area coloured greeny-blue?  It's the area either side of a stream but does it denote marshy ground, low-lying ground?

(2) the yellow line marked SOS lines (or could it be 505 lines?) - clearly they don't relate to any feature on the ground, but what could they be?

Many thanks!

[Dai Bach y Sowldiwr]

Altitude.
Below the 70 (Metre/ft?) contour.

[TEW]

My understanding of SOS lines is that if the SOS signal is given (perhaps by flares) the enemy are being aggressive on the SOS lines and therefore fire should be laid down on the SOS lines.

Remember, this could be at night or in thick fog when the SOS lines are not visible. It would be imperative to have the lines registered and be able to bring MG or mortar fire on the SOS lines blind so to speak.

I was in Croisilles in early Oct and although the blue area matches the contour line and presumably a sort of flood plain the stream is not exactly substantial enough to make much of it marshy.

TEW

[brianmorris547]

The same map (and others) appears in the May 1917 WD of 100 Infantry Brigade (33 Div) and there are lots of reports re 20/05/1917 and attached papers on which there might be something. I could not see anything obvious. I will have a look at 33 Div HQ and 33 Div RE WDs.

Brian

EDIT: I could not see the map in the WD of 9 HLI so you must have read the Brigade WD. Apologies.

Edited Friday at 15:45 by brianmorris547
typo

[BearsdenWarMem]

7 hours ago, Dai Bach y Sowldiwr said:

Altitude.
Below the 70 (Metre/ft?) contour.

That would make perfect sense - a quick visual guide to lower-lying ground.  Thank you!  I'm disappointed my O Level Geography (Grade B) didn't help me with that one ..

[BearsdenWarMem]

6 hours ago, TEW said:

My understanding of SOS lines is that if the SOS signal is given (perhaps by flares) the enemy are being aggressive on the SOS lines and therefore fire should be laid down on the SOS lines.

Remember, this could be at night or in thick fog when the SOS lines are not visible. It would be imperative to have the lines registered and be able to bring MG or mortar fire on the SOS lines blind so to speak.

I was in Croisilles in early Oct and although the blue area matches the contour line and presumably a sort of flood plain the stream is not exactly substantial enough to make much of it marshy.

TEW

Thank you, I had not heard of SOS lines before but it makes good sense for pre-agreed areas of artillery fire.

I'm jealous of you getting to Croisilles but I agree, having seen the map I was then pretty surprised to see the 'river' on Google Street View!  I've posted my profile of the man who died in the attack, the links here in case you're interested:

https://bearsdenwm.blogspot.com/2024/11/james-theodore-boyack.html

Be warned the first half is about his early life in Glasgow and the main audience is local people so it is not a profound work of military history.  I have just found some reports in the battalion war diary and a better map in the brigade war diary so sill be updating it over the next few days.  But if your local knowledge suggests anything else, please let me know.

Thanks again!

[BearsdenWarMem]

5 hours ago, brianmorris547 said:

The same map (and others) appears in the May 1917 WD of 100 Infantry Brigade (33 Div) and there are lots of reports re 20/05/1917 and attached papers on which there might be something. I could not see anything obvious. I will have a look at 33 Div HQ and 33 Div RE WDs.

Brian

EDIT: I could not see the map in the WD of 9 HLI so you must have read the Brigade WD. Apologies.

You are absolutely right, Brain, I had started with the battalion diary, switched to the brigade and then forgot which file I was looking at.  And you're right, I have more work to do - the current version of the day's events are covered in three short paragraphs:

https://bearsdenwm.blogspot.com/2024/11/james-theodore-boyack.html

The main audience is interested local people so I can't go into too much detail, but thanks for your guidance, it's appreciated.

That reminds me, I also saw a lot of aerial reconnaissance photos in the Brigade War Diary - do you know of any way to match them to the area I am interested in (north-east of Croisilles)?

My best wishes, Andrew

[Old Forge]

12 hours ago, BearsdenWarMem said:

Thank you, I had not heard of SOS lines before but it makes good sense for pre-agreed areas of artillery fire.

Hi Andrew,

In difficult periods the battery or batteries allocated to an SOS line might remain laid and loaded for a quick response. The NATO equivalent is Final Protective Fire (FPF).

Cheers,

Richard

[Howard]

The green areas are part of a hypsometric tinting applied locally by water colour. Such tinting is used to show elevation, something not that easy to do on a 2D map. There are several schemes that attempt to show elevation, e.g. contour lines, hachuring or hypsometric tinting; sometimes all 3 are used on the same map, even on modern times.

When I scanned the IWM’s collection of Great War maps, it became clear the problem of depicting elevation was a great concern at the time, some maps have the tinting overprinted as part of the map (slow and expensive), some coloured in water colour and some in pencil. General Haig even had 3D maps produced by pasting successive layers on card. I think they would have liked Google Earth at the time!

On printed maps a repeated symbol is used to show marshy ground but even the keenest water colourist did not usually use those in the war.

Howard

[battle of loos]

Good morning,

Here is an overlay of the 2nd card. :

 

Kind regards

michel

[BearsdenWarMem]

7 hours ago, Howard said:

The green areas are part of a hypsometric tinting applied locally by water colour. Such tinting is used to show elevation, something not that easy to do on a 2D map. There are several schemes that attempt to show elevation, e.g. contour lines, hachuring or hypsometric tinting; sometimes all 3 are used on the same map, even on modern times.

When I scanned the IWM’s collection of Great War maps, it became clear the problem of depicting elevation was a great concern at the time, some maps have the tinting overprinted as part of the map (slow and expensive), some coloured in water colour and some in pencil. General Haig even had 3D maps produced by pasting successive layers on card. I think they would have liked Google Earth at the time!

On printed maps a repeated symbol is used to show marshy ground but even the keenest water colourist did not usually use those in the war.

Howard

Howard, thank you for taking the time to explain.  Looking at the ground on Google Street View there seems to be no cover at all (I have no military training so might not be seeing it).  Faced with a 600 yard advance uphill to the Hindenburg Line I imagine they were desperate for any tiny advantage they could get from the ground.  thanks again. Andrew

[BearsdenWarMem]

5 hours ago, battle of loos said:

Good morning,

Here is an overlay of the 2nd card. :

 

Kind regards

michel

Michel, this is brilliant, thank you!  I have posted my work-in-progress on my website but would love to have your permission to include this image.  The website is not commercial (just the opposite!) and I would be happy to attribute the work to you:

https://bearsdenwm.blogspot.com/2024/11/james-theodore-boyack.html

You need to scroll to about half way through to get to 1917.

Andrew

[battle of loos]

good evening,

There is no problem with the card.
I simply used your map with Google Earth and the result is there.
I have a friend who lived in Fontaine les Croisilles so I know a little about the area.
This village and the blue area on the map are in a basin.

Kind regards

michel

[TEW]

I only know about SOS lines as a result of an early post of mine.

https://www.greatwarforum.org/topic/133173-mg-rangingtarget-board/

TEW

[Old Forge]

Hi @TEW, your earlier post makes fascinating reading! I’ll add some thought in it although it’s an old thread.

Cheers,

Richard