Background

Michael Dorosh kindly provided (for my old website on counterbattery) the following information from the Canadian Army Training Memorandum No. 24, March 1943, which came as a welcome piece of information to me, since I understood the theatre grid system of the Commonwealth armies, but had never even thought about how the Germans did it.  Turns out they used a Stosslinie, thrust line (or point), drawn on a map.  This is a variant of the offset method, in which a location is expressed by giving the distance to two edges of the map – except that the distance is given in relation to a randomly chosen line on the map.

The differences in locating units on the map were quite astounding to me, and I originally wondered why the Germans ever came up with such an unwieldy system.  But I guess that in application it is not actually unwieldy, and it has the advantage to add to secrecy. While David Irving claims that Rommel invented this system to help his tanks advance in France, I simply doubt that this is true, since it appears to be a universally used system in the Wehrmacht.

The header carried by the document is preserved in this post. The Allied armies put out this kind of information to inform their soldiers about the capabilities of the German forces. The most famous of these may well be the manual to the 8,8cm AA gun published by the US Army. A lot of these information leaflets are published at the excellent Lone Sentry website.

NOT TO BE PUBLISHED The information contained in this document is not to be communicated, either directly or indirectly, to the Press or to any person not holding an official position in His Majesty’s Service. **

THE GERMAN MAP REFERENCE

1. The Germans have a map reference system which they call “stosslinie”, which means “thrust point.” A line is drawn on a map. Theoretically, it may run in any direction, but in practice it is found to run either in the direction of the German intended advance or down the axis of a reconnaissance unit.
2. The line begins at a fixed point and continues indefinitely in the required directions. For convenience it is usually divided into centimeters. To give a map reference, a perpendicular is dropped from the reference point to the thrust line. Measurements are then given from the starting point of the line to the point where the perpendicular cuts the thrust line; then along the perpendicular to the reference point. Since the point may lie on either side of the thrust line, the second figure has to be prefaced by either right or left as one looks toward the enemy.
3. A typical reference would be 12 right 3.5. The figures always are centimeters; therefore, the actual distance on the ground represented by each unit will NOT always be the same but will vary according to the scale of the map.
4. In order to make the code more secure, the following variations may occur:

1. The scale may start with an arbitrary figure; that is, the starting point may be called sixty instead of zero; so that our map reference would read 72 right 3.5.
2. Dummy figures are often used. By previous arrangement, it is agreed that the first, third and fifth figure of any map reference will be dummies. The above map reference, for instance, might be given as 87329 right 83359.
3. Finally when more than one thrust line is being used, perhaps by a Corps or Army, they are numbered and map references begin with the number of the thrust line.

5. Instruments have been found that consists of a rule in translucent material graduated in millimeters, with a shorter ruler similarly graduated, fixed at right angles which slides up and down on the larger ruler.
6. Operators with practice can give references very quickly.

The US Army also issued an explanation of the system to its soldiers.

Excerpt from chapter 14 of “Artillery in the Desert”, Military Intelligence Service, Special Series No. 6, November 1942:

One of the most interesting methods of enabling map references to be sent in the clear with security is the “thrust line” method used by the Germans. (This method is similar to the code described in FM 18-5, “Organization and Tactics of Tank Destroyer Units,” June 16, 1942, paragraph 231 b (2) (e).) It consists of a line drawn upon a map which theoretically may run in any direction but which actually usually extends in the proposed direction of advance or down the axis of a reconnaissance unit.

The line, which begins at a fixed point and continues indefinitely in the required direction, is usually divided into centimeters for convenience. To give a map reference, a perpendicular is dropped from the reference point to the thrust line. Measurements are then taken from the point of origin to the point where the perpendicular cuts the thrust line, then along the perpendicular to the reference point. Since the point may lie on either side of the thrust line, the second figure must be prefaced by either “right” or “left”, as one looks toward the enemy.

A typical reference would be “6 right 3.” (See fig. 15.) The figures are always in centimeters; therefore, the actual distance on the ground will vary with the scale of the map used. The scale may start with an arbitrary figure, and have dummy figures interspersed, or it may start with the number of the thrust line when there are several in a given area. These devices make the code difficult to break rapidly.

Thrust Point – From http://www.lonesentry.com

Figure 15.–The “thrust line”

Instruments have been found consisting of a transparent ruler graduated in millimeters, with a shorter ruler similarly graduated and fixed to slide up and down at right angles to the longer ruler. Practiced operators can give references very quickly.

The whole document is worth reading, by the way.

Here is an example order fixing a thrust line, which I found in the files of 21st Panzer Division.

Order from Panzergruppe Afrika fixing a Thrust Line. Rommelsriposte.com Collection

Secret Command Affair

German Africa Corps                                       CP, the 16 November 41
Operations Section                                          17 copies
No. 1274/41 secret Command Affair       12th Copy

Re: Thrust Line

To:

Distribution List

For the map Libya 1:400,000, German “preliminary special issue I 1941” (Leaf Bardia), the following thrust line is ordered:
A = 0 = Gr. el Arid (near Trigh Enver Bel, 50km west of Bardia)
B = 15.8 = Gr. el Abd (14km south of Sidi Omar)

For the German Africa Corps

The Chief of the General Staff

Utility

The use of a temporary, operation-dependent system is very different from the Commonwealth system, which used a permanent ‘theatre’ grid superimposed on a map of the area of operations, or even wider. The UK National Archives website explains it quite well at this link.  This system had originally developed in World War I (World War I was to the artillery what the French revolution was to politics), and the development during the war to end all wars is very well charted at this link. Locations on the map would be expressed through two numbers with identical but variable length. The longer the number, the more precise the location information. Information on this can be found on Nigel Evan’s site at this link.  This system, or one like it, is now universally used by the western armies at least.

Practice in North Africa

In North Africa, the thrust line was determined by Panzergruppe HQ during CRUSADER, and my guess is that this did not change when the HQ was upgraded to army status.  I believe that in other theatres thrust lines were determined by Corps HQs (a Panzergruppe was equal in status to a Corps HQ), but I am not certain about this.   During CRUSADER I have come across two changes of Panzergruppe’s thrust line, but there may have been more. There is also a good discussion on the system at this link.

So, in the German system, a unit would report something like this, and the note below explains it:

Following executed relief CAM* assembled, with Ariete in area around 48.5 left 4.5, with Trieste around 48.5 left 5.5. CP CAM from 17 January 10h00 48.5 left 5.

 

The shows a Stosslinie on an Italian map used by the German intelligence officer in Panzergruppe Africa’s command staff. The line starts with the value of 65 north of B. el Harmarin/south-east of Mechili, and ends with the value of 105 at Bir el Gobi. Rommelsriposte.com Collection

Notes

*Corpo Armata di Manovra (Mobile Army Corps, not Mobile Armoured Corps as one reads sometimes!), the later XX Corps in the Italian army, consisting of the Ariete armoured and Trieste motorised divisions and the RECAM reconnaissance detachment.

**Since His Majesty is dead, I guess I have been released from that obligation….