Six-digit MPI entries in WWII Eighth Air Force field orders

Chuck Varney
21 Apr 18


Background

In 2013 Tom Harrison published a book, “Kassel”, that purported to explain how a navigational error occurred that caused the Eighth Air Force’s 445th Bomb Group to suffer great loss of aircraft and crews on a 27 September 1944 bombing mission to Kassel, Germany. He built his explanation around a claim that the first six digits of a field order MPI entry of the form 070058/14 represented a pair of GEE-H distances, and that MPI meant “mean point of intersect” (rather than the correct “mean point of impact”). He then took the asserted GEE-H distances and wove them into a story, which—for him—explained the cause of the navigational error. I found his initial claim, and all his subsequent explanations of equipment operation that enabled the navigation error, to be demonstrably wrong.

I was left wondering how to properly decipher an MPI entry like 070058/14. I suspected that 070 and 058 were grid map coordinates and speculated that “/14” was a chart, sheet, or book reference related to the grid. I searched for, but failed to find, field orders for other Eighth Air Force mission that might shed some light.

April 2018

Kassel revisted

 I revisited the MPI 070058/14 entry, looking for grid maps used in the European Theater.  Thierry Arsicaud’s echodelta.net site provides a Nord de Guerre zone grid map that covers Germany, and a coordinate translator that enables conversion from Nord de Guerre coordinates to geographic coordinates (latitude and longitude). I used them to determine that Kassel, Germany lies in Nord de Guerre grid rC, and then used the coordinate translator to find the geographic coordinates corresponding to the four 6-digit MPI’s given in the Field Order No. 470 excerpt shown in Figure 1. The results are plotted in Figure 2.



Figure 1
. Excerpt from 2nd Bomb Division Field Order No. 470 for the Kassel 27 September 1944 mission




Figure 2. Plot of the 2nd Bomb Division target area (Henschel and Son Works, in red rectangle and MPI's (red diamonds) for the
               27 September 1944 Kassel mission


The plotted MPI's lie well to the west of the target area; for example, rC070058 is about 14.7 km west and 0.9 km north of the three buidings that show up as white rectangles within the red target rectangle. If
the MPI digits are Nord de Guerre coordinates, as assumed, something in the "/14" MPI suffixes, either alone or in combination with the GH 637C,D, and E target packages, is required to put the actual MPI’s into the target rectangle.

Eighth Air Force 24 December 1944 missions

I searched for other Eighth Air Force field order examples in the hopes that they might provide further insight into the MPI entries. I found a gold mine in Joost de Raaf’s detailed documentation of the Eighth Air Force missions flown on 24 December 1944 by the 1st, 2nd, and 3rd bomb divisions. In it, he has collected 86 pages of field orders, supplements, and annexes, distributed among the three bomb divisions. I extracted the MPI portion of division-level field orders as shown in Figures 3., 5., and 7., below. I used the same process as described in Kassel revisited to determine appropriate Nord de Guerre grids, and to plot MPI's and target areas on Google Earth. For the intended primary targets I used this Eighth Air Force Historical Society page, where 1. lists six 3rd Bomb Division targets, 2. lists five 1st Bomb Division targets, and 3. lists fourteen 2nd Bomb Division targets.

1st Bomb Division, 24 December 1944



Figure 3. Excerpt from 1st Bomb Division Field Order No. 587 for 24 December 1944



Figure 4. Plot of 1st Bomb Division target locations (yellow circles) and MPI’s (red diamonds).

Only five of the 15  MPI's of Figure 3. are plotted in Figure 4. because 14 of them fall within the white rectangle and would be unreadable if plotted. The four shown in the rectangle mark the most northern, southern, eastern, and western of the 14.

Unlike the Kassel example that had only a single suffix, "/14", for the given MPI's, here there are three different ones: "/1", "/2", and "/4".



2nd Bomb Division, 24 December 1944
 

Figure 5. Excerpt from 2nd Bomb Division Field Order No. 554 for 24 December 1944




Figure 6.
Plot of 2nd Bomb Division target locations (yellow circles) and MPI’s (red diamonds).



Twelve of the 13 plotted MPI's fall on the given target locations--and the 14th is close to one, making it clear that the 6-digit MPI's are Nord de Guerre coordinates.

For more, see the Discussion section, below.

3rd Bomb Division, 24 December 1944



Figure 7. Excerpt from 3rd Bomb Division Field Order No. 526 for 24 December 1944



Figure 8. Plot of 3rd Bomb Division target locations (yellow circles) and MPI's (red diamonds)

The five MPI's given in Figure 7. plot as a group to the south and west of the target locations. Four have suffix "/2"; one has "/4".

Discussion

The field orders for the 27Sep44 Kassel mission and those of the 1st and 3rd  Bomb Division for the 24Dec44 missions have 6-digit MPI entries that terminate in either  "/1", or "/2", or "/4", or "/14".  I found nothing in the collected field orders that indicates what any of those suffixes mean.

By assuming for these three examples that the first six digits in an MPI entry are Nord de Guerre east and north coordinates, and--by knowing the target coordinates--put them in the appropriate grid block, the MPI's plot in the general vicinity of the targets. Except for three of the Kassel MPI's, the plotted MPI's can't be made to fall on targets by simple translation in the east-west and north-south directions. As a result, I can't say for certain the MPI entries are Nord de Guerre coordinates, and how to exactly decipher the entries remains unknown.

The data for the 2nd Bomb Division (2BD) is a different matter. For it, the MPI entries plot directly--and correctly--on the targets. Unlike the other examples discussed, the 2BD documents do not have any instances of  "/x" or "/xy" MPI suffixes. They do have an associated entry: either S1 or T1. These are explicitly referred to as sheets in a few instances.

All 14 of the 2BD 6-digit MPI's have the same entry in the TARGET column: GSGS4416. Internet searches revealed that this was a British War Office map series designation, where GSGS stands for General Staff Geographic Section. G.S.G.S. 4416 was a 1:100,000 scale set covering central Europe. Sheets T.1. and S.1. were sheets in that set.


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