Geoffrey Sinclair
2014-07-02 15:21:54 UTC
Most of this data comes from the 8th Air Force April 1945 monthly
report, which includes 2 tables of effort, one for the B-17 and one
for the B-24, it notes casualty figures are not finalised as some
reports still have to come in from aircraft that landed in Europe,
not back in Britain.
For example it seems the total number of heavy bombers written
off after a combat sortie is 1,557 versus 1,562 in the April report.
In addition the sorties are for stated to be bombing missions only,
however the final 8th Air Force report has slightly higher sortie
figures, 330,866 versus 328,590 in the April report, so if a final
report can be found that splits B-17 and B-24 effort the numbers
will vary slightly from the ones presented here.
In terms of numbers the B-17 accounts for 68.9% of all 8th Air Force
heavy bomber sorties, 69.2% of such sorties that entered contested
airspace (credit sortie) and 70.2% of sorties reported as bombing
(effective sortie). The average B-17 bomb load for the war was
5,139.4 pounds versus 5,329.95 pounds for the B-24. It means the
B-17 dropped 69.45% of the bombs dropped by the 8th Air Force
heavy bombers.
As can be seen by the sortie percentages it seems the B-24 was
more vulnerable at about every stage to factors causing the sortie
to be abandoned. One reason seems to be a different use of
spare sorties, aircraft taking off used to replace any aborting
sorties, so formation left Britain at full strength. Some 4,621 B-17
sorties landed classified as "unused spares" versus 302 B-24,
which probably accounts for some of the later differences in
sortie abort rates.
Having said that some 91.4% of B-17 credit sorties were
classified as effective, versus 87.1% for the B-24. So while 68.9%
of heavy bomber sorties were B-17s they accounted for 61.95%
of mechanical, 58.7% of weather and 61.45% of other reason
aborted sorties. The B-17 was the more reliable as used by the
8th Air Force.
For 1944 and the first 4 months of 1945 the B-24 had an accident
rate on operations of 0.3 per 100 take offs and 1.01 accidents per
1,000 hours of non operational flying, versus 0.22 and 0.97
respectively for the B-17.
For the entire war 1.58% of B-17 credit sorties were Missing In
Action, versus 1.2% of B-24, partly this is the result of the losses in
1943 (nearly a quarter of total B-17 losses) but if you simply use
the 1944 results the loss figures actually increase, to 1.61% for the
B-17 and 1.3% for the B-24. So unless the B-24 was deliberately
and regularly being sent to less heavily defended targets the figures
indicate you were more likely to come home in a B-24.
Another interesting point about losses is for every 4.15 B-17
listed as missing another was written off after a combat sortie,
for the B-24 it is 3 missing for each write off.
The loss figures at first examination seem to be saying the
opposite to the anecdotal evidence, the figures are reporting
the B-24 was the more survivable, taking fewer losses and
making it back with heavier damage. Alternatively in the
damaged situation it could be the B-24 was more prone to
taking significant damage in a crash landing. The figures
indicate this was the case, 0.5% of B-17 credit sorties
were written off, versus 0.6% of B-24, some 20% more than
the B-17 but the B-17 missing to write off ratio is approaching
40% more than the B-24.
So short of a systematic bias in target selection the B-24 was
more likely to abandon the mission and more likely to crash but
more likely to bring you back, even when damaged, even when
accounting for it taking more damage in a crash landing.
The USAAF had 4 categories of damage,
A, repairable within 36 hours by the unit,
AC, more than 36 hours to repair and needing non unit resources
like a sub depot,
B requiring a full Repair Depot to fix
E write off.
For the war, using 293,025 credit sorties, there were 43,601
category A, 13,893 category AC, 593 category B and 1,557
category E, or 20.4 of all credit sorties came back damaged
enough to be classified as damaged. By year it was 27.4%
in 1942, 30.9% in 1943, 21.1% in 1944 and 15.6% in 1945.
The top 4 months were all in 1943 and are the only figures
above 40%, being 48.4% in January, 43.9% in July, 42.4%
in August and 41.7% in October. Being percentages these
figures are prone to big shifts when there are only a small
number of sorties, in 1943 there were 22,099 heavy bomber
credit sorties, versus 188,036 in 1944 and 81,912 in the
first 4 months of 1945. There were only 279 credit sorties
in January 1943, but over 2,000 for the other 3 months
listed above.
The night bombers consistently reported higher MIA figures
than the day bombers for 1945, as a percentage of sorties,
but it seems the number damaged, including to write off
stage, was around 2.8% of sorties despatched. Versus
15.6% for the 8th Air Force credit sorties, which were about
90% of airborne sorties. The extra maintenance requirements
from consistently having several times the number of damaged
aircraft would have been significant.
Geoffrey Sinclair
Remove the nb for email.
report, which includes 2 tables of effort, one for the B-17 and one
for the B-24, it notes casualty figures are not finalised as some
reports still have to come in from aircraft that landed in Europe,
not back in Britain.
For example it seems the total number of heavy bombers written
off after a combat sortie is 1,557 versus 1,562 in the April report.
In addition the sorties are for stated to be bombing missions only,
however the final 8th Air Force report has slightly higher sortie
figures, 330,866 versus 328,590 in the April report, so if a final
report can be found that splits B-17 and B-24 effort the numbers
will vary slightly from the ones presented here.
In terms of numbers the B-17 accounts for 68.9% of all 8th Air Force
heavy bomber sorties, 69.2% of such sorties that entered contested
airspace (credit sortie) and 70.2% of sorties reported as bombing
(effective sortie). The average B-17 bomb load for the war was
5,139.4 pounds versus 5,329.95 pounds for the B-24. It means the
B-17 dropped 69.45% of the bombs dropped by the 8th Air Force
heavy bombers.
As can be seen by the sortie percentages it seems the B-24 was
more vulnerable at about every stage to factors causing the sortie
to be abandoned. One reason seems to be a different use of
spare sorties, aircraft taking off used to replace any aborting
sorties, so formation left Britain at full strength. Some 4,621 B-17
sorties landed classified as "unused spares" versus 302 B-24,
which probably accounts for some of the later differences in
sortie abort rates.
Having said that some 91.4% of B-17 credit sorties were
classified as effective, versus 87.1% for the B-24. So while 68.9%
of heavy bomber sorties were B-17s they accounted for 61.95%
of mechanical, 58.7% of weather and 61.45% of other reason
aborted sorties. The B-17 was the more reliable as used by the
8th Air Force.
For 1944 and the first 4 months of 1945 the B-24 had an accident
rate on operations of 0.3 per 100 take offs and 1.01 accidents per
1,000 hours of non operational flying, versus 0.22 and 0.97
respectively for the B-17.
For the entire war 1.58% of B-17 credit sorties were Missing In
Action, versus 1.2% of B-24, partly this is the result of the losses in
1943 (nearly a quarter of total B-17 losses) but if you simply use
the 1944 results the loss figures actually increase, to 1.61% for the
B-17 and 1.3% for the B-24. So unless the B-24 was deliberately
and regularly being sent to less heavily defended targets the figures
indicate you were more likely to come home in a B-24.
Another interesting point about losses is for every 4.15 B-17
listed as missing another was written off after a combat sortie,
for the B-24 it is 3 missing for each write off.
The loss figures at first examination seem to be saying the
opposite to the anecdotal evidence, the figures are reporting
the B-24 was the more survivable, taking fewer losses and
making it back with heavier damage. Alternatively in the
damaged situation it could be the B-24 was more prone to
taking significant damage in a crash landing. The figures
indicate this was the case, 0.5% of B-17 credit sorties
were written off, versus 0.6% of B-24, some 20% more than
the B-17 but the B-17 missing to write off ratio is approaching
40% more than the B-24.
So short of a systematic bias in target selection the B-24 was
more likely to abandon the mission and more likely to crash but
more likely to bring you back, even when damaged, even when
accounting for it taking more damage in a crash landing.
The USAAF had 4 categories of damage,
A, repairable within 36 hours by the unit,
AC, more than 36 hours to repair and needing non unit resources
like a sub depot,
B requiring a full Repair Depot to fix
E write off.
For the war, using 293,025 credit sorties, there were 43,601
category A, 13,893 category AC, 593 category B and 1,557
category E, or 20.4 of all credit sorties came back damaged
enough to be classified as damaged. By year it was 27.4%
in 1942, 30.9% in 1943, 21.1% in 1944 and 15.6% in 1945.
The top 4 months were all in 1943 and are the only figures
above 40%, being 48.4% in January, 43.9% in July, 42.4%
in August and 41.7% in October. Being percentages these
figures are prone to big shifts when there are only a small
number of sorties, in 1943 there were 22,099 heavy bomber
credit sorties, versus 188,036 in 1944 and 81,912 in the
first 4 months of 1945. There were only 279 credit sorties
in January 1943, but over 2,000 for the other 3 months
listed above.
The night bombers consistently reported higher MIA figures
than the day bombers for 1945, as a percentage of sorties,
but it seems the number damaged, including to write off
stage, was around 2.8% of sorties despatched. Versus
15.6% for the 8th Air Force credit sorties, which were about
90% of airborne sorties. The extra maintenance requirements
from consistently having several times the number of damaged
aircraft would have been significant.
Geoffrey Sinclair
Remove the nb for email.