Piercing the Fog - Air Force Historical Studies Office

Building an Air Intelligence Organization
analysis and, correlating it with economic data from such agencies as MEW and
BEW, attempted to determine the impact of the lost production or repair
capability on the German war effort.
Damage assessment was fundamental to the conduct of precision bombing
since it influenced decisions on which targets to strike, at what intervals, and
with what forces. The entire process was fraught with difficulty and uncertainty.
In the first place, it depended on prior intelligence about the nature and overall
condition of the German economy, which was itself incomplete and in some
fundamental ways inaccurate. It involved assumptions, derived from macroeconomic
analysis, about the relative importance of individual targets within broad
target categories. In a more technical sense, postattack analysis, often limited
to aerial photographs taken tens of thousands of feet above the target, had to
differentiate between the more apparent physical damage done to the structures
themselves and the real impact of such damage on the capabilities of the target
(i.e., production output and repair capability). Additionally, the amount of time
required for the enemy to repair any given facility was at best an educated
guess.
In time, ULTRA would contribute significantly to the Allied analytical
capability by supplementing photographic evidence, suggesting new perspectives
on such evidence, or offering information unobtainable from the air.
Although few of the photointerpreters at Medmenham were aware of it because
of the tight compartmentalization of ULTRA, data regularly flowed between the
code breakers and intelligence officers at BP and the CIU.1’8 In early American
bombing operations, ULTRA did not contribute greatly to damage assessments
because the Germans sent most of the information necessary to evaluate the
effect of bombing by land lines and through civilian channels. Reports subject
to ULTRA interception were often based on first impressions, when the rubble
had not yet been cleared and actual damage not fully determined. Too,
individuals sending postattack reports had reasons for either exaggerating or
downplaying the extent of the damage.’”
Damage assessment became increasingly proficient over time. Interpreting
physical damage was always easier than extrapolating the impact of the damage
on the target’s output or the effect of that result on the enemy’s overall
industrial production, and thus military capability. Two examples from this
early period of operations illustrate the difficulties involved. On March 22,
1943,73 B-17s of the 91st, 303d, and 305th Bomb Groups dropped 536 1,000pound
bombs on the submarine construction yard at Vegesack. Eaker wrote
jubilantly to Arnold that RAF postattack evaluation had determined, in Eaker’ s
words, “the Vegesack yard has been put out for a year by one raid of less than
100 heavy bombers.”’20 Supporting the RAF assessment was a Royal Naval
Intelligence Division (NID) report that noted severe damage to several
submarines as well. A follow-on NID evaluation the next month revealed that
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