Geoffrey Sinclair
2014-09-25 14:41:59 UTC
Tonnage is in short tons, 2,000 pounds.
The 15th Air Force was officially formed on 1 November 1943,
with 4 B-17, 2 B-24, 1 B-25 and 3 B-26 groups. The B-25
group was reassigned to the 12th Air Force on 3 November, the
B-26 groups on 1 January 1944. For fighter cover there were
3 P-38 and 1 P-47 groups.
Final strength was 6 B-17 and 15 B-24 groups, along with 3
P-38 and 4 P-51 groups, with the 332nd fighter group having
4 squadrons of P-51s instead of the normal 3.
No new units became operational in 1943, two new B-24
groups flew their first mission on 8 January 1944, another on
the 30th, February saw three more B-24 groups flying their
first missions on the 8th, 10th and 12th, March had 1 new
B-17 group (on the 30th) and 2 B-24 groups, on the 2nd and
19th, four new groups in April, a B-17 on the 12th and 3 B-24
on the 2nd, 29th and 30th, finally in May 2 new B-24 groups
flew their first missions on the 5th and 10th.
A P-51 group was transferred from the 12th Air Force and
flew what is reported to be the first P-51 operation in the
Mediterranean as its first 15th Air Force mission on 16
April. Another P-51 group was transferred from the 12th
and flew its first 15th Air Force mission on the 10th of May.
The original P-47 group, the 325th, converted to P-51 in
May 1944, last P-47 operations on the 24th, first P-51 on
the 27th. Finally the 332nd fighter group was transferred
to the 15th Air Force while it was converting from the P-39
to the P-47, it flew P-47 operations from 7 to 30 June while
converting to P-51s, with the first P-51 operation on 4 July.
It is clear that in mid May 1944 the 15th Air Force had a real
fighter shortage, 21 bomb to 6 fighter groups, finally ending
up with 7 fighter groups.
At the other end of the campaign, 2 B-24 groups were
returned to the US in mid April 1945, while by the end of
May 1945 another 4 B-24 groups had been returned to
the US and another 4 assigned to Air Transport Command
in Natal, Trinidad and Casablanca. Planning as of the
end of May 1945 was that only 3 of the original B-17 groups,
the 2nd, 97th and 99th, would remain in Europe, the rest of
the bomb groups would be returned to the US by end July,
followed by the fighter groups.
This follows the pattern in the 8th Air Force, the rapid
retirement of the B-24 while retaining the B-17.
Overall the B-17 accounts for 31.5% of all airborne 15th Air
Force heavy bomber sorties, but 32.5% of effective sorties,
that is they completed the mission. As with the 8th Air Force
a number of airborne sorties were spares to replace any
aborting aircraft, unused spares were classified along with
any early aborts as Early Return, or Non Sorties, the B-17
accounts for 32.4% of such sorties. The B-17 accounts for
28.5% of aborts due to weather, 26.1% due to mechanical
problems, 22.7% for aircraft and accessory problems, 19%
for lead ship failure (radar bombing) but 38.7% of
miscellaneous reason aborts, overall 19.9% of B-17 and
23.3% of B-24 sorties were non effective.
Clearly the number of early returns is influenced by the number
of spare sorties and the number of lead ship failures by the
amount of radar bombing, but overall it is seen the B-17 was
the more reliable. In addition overall around 77% of B-17 were
operational at any one time versus 69% of B-24s.
Weather aborts are broken down into two categories, target
obscured and failed to reach target. From January 1944 on
8,664 fighter and bomber sorties found the target obscured,
12,380 failed to reach the target.
The 15th Air Force first used H2X to aim bombs on 15 April
1944, against Bucharest, and unfortunately the different
references disagree about what attacks used H2X. As the
analysis currently stands from 15 April to end October 1944
there were 2,988 effective B-17 and 3,764 effective B-24
sorties using H2X, plus 8 B-17 and 3 B-24 effective sorties
using H2X at night. For the remainder of the war there are
around another 20,000 day and 150 night effective sorties
using H2X.
When it comes to losses the B-17 was 32.2% of heavy bombers
reported lost to enemy aircraft, 23.3% to flak, 25% to mechanical
or other reasons, and 26.6% of unknown cause losses. As a
percentage of effective sorties, B-17 loss rate was 1.5%, the
B-24 2%. The B-17 had 34.2% of heavy bomber encounters
with enemy aircraft, that is 4,531 versus 8,703 for the B-24. So
overall it appears to have been slightly less vulnerable to fighter
attack and definitely less vulnerable to flak and equipment failure,
but as "unknown cause" makes up 14.7% of reported losses the
results have a significant error margin.
For every bomber lost on operations another 5.25 were listed
as damaged, for the B-17 it was 6.9 damaged to destroyed,
for the B-24 5.1 to 1, implying the B-24 took less damage to
shoot down or was being systematically sent to more lightly
protected targets. There seems to be a bias at times to use
higher flying B-17 units on heavily defended targets, but how
much this matters over the course of the campaign is another
matter.
However the large number of sorties to mainly communication
targets in Italy disguises the loss rates, both oil and industry
targets, mainly outside Italy, had an aircraft loss rate of 3.1%.
The personnel loss records have 3.8% of casualties in the
Adriatic, which could mean from missions against a number of
countries, plus 5% of casualties to "other countries", in both
cases bomb tonnage dropped is zero. With that in mind targets
in Austria are reported as having been attacked by 24% of bombs
dropped and resulted in 24.2% of casualties (killed, wounded,
missing, PoW), Germany 11.6% of bombs, 14.1% of casualties,
Romania 8.5% of bombs, 9.8% of casualties, Italy 29.4% of
bombs, 18.2% of casualties and surprisingly Yugoslavia with
7.1% of bombs but 12.9% of casualties.
Accidents on non operational sorties lost 43 B-17 and 192 B-24.
The 15th Air Force uses destroyed and missing categories for
aircraft losses on operational missions, it is clear most destroyed
aircraft would be classified as missing in the system used by
the 8th Air Force, so no comparison is possible when it comes to
aircraft that returned to friendly territory too damaged to be repaired
versus those lost over enemy territory.
Unfortunately while there are figures for the total number of
sorties by B-17 and B-24 for the campaign so far no official
campaign total of bomb tonnage by aircraft type has been found.
Monthly figures for bomb tonnage by type are available from
January 1944 on but not sorties by type. In addition some key
reports use pilot sorties which are all sorties that crossed
enemy lines, whether effective or not, which means they
cannot be used to calculate bombs dropped per effective sortie.
The B-17 dropped 104,877 tons of bombs January 1944 onwards,
the B-24 192,113 tons, B-17 effective sorties from November
1943 onwards are 41,751, B-24 86,838. Even with the missing
bomb tonnage it is clear the B-17 was carrying the heavier loads
on average.
To obtain an idea on average bomb loads the data in the "Target
and Duty Sheets", which give a break down by bomb group, have
been used even though they are only available for the December
1943 to October 1944 period at the moment and the December
1943 figures do not include tonnage classified as jettisoned.
For effective B-17 sorties December 1943 to October 1944 the
average bomb load dropped was 5,400 pounds, for B-24 it was
4,690 pounds. These figures are a slight underestimate, as
some sorties classified as effective have at least some of
their bomb tonnage classified as jettisoned.
On an administrative note the number of effective sorties used in
the above calculation excludes 58 B-17 PoW evacuation sorties
in August and September 1944 and 659 B-24 supply mission
sorties to France in September and October 1944 as well as
a small number of reconnaissance and air sea rescue sorties.
The jettisoned bomb tonnage listed in the Target and Duty
Sheets is significant, for January to October 1944 it is 16,777
tons versus 182,185.6 tons dropped by effective sorties. Most
jettisoned tonnage is that, but some appears to be bombs
that for example hung up but later dropped or were dropped
clear of any recognised target, "unaimed" bombs perhaps.
As a sanity check the results can be compared with the USAAF
Statistical Digest figures, firstly for airborne heavy bomber sorties
in the Mediterranean theatre, month, duty sheets, digest,
Jan-44 \\ 4778 \\ 4,720
Feb-44 \\ 3974 \\ 3,981
Mar-44 \\ 5997 \\ 5,996
Apr-44 \\ 10171 \\ 10,182
May-44 \\ 14425 \\ 14,432
Jun-44 \\ 11737 \\ 11,761
Jul-44 \\ 12656 \\ 12,642
Aug-44 \\ 12197 \\ 12,194
Sep-44 \\ 10081 \\ 10,056
Oct-44 \\ 9645 \\ 9,567
January sorties include 11 Air Sea Rescue, March include 1 weather
reconnaissance, July include 7 photo reconnaissance, August include
4 photographic reconnaissance, 1 special mission, 1 secret mission,
38 PoW evacuation, September include 20 PoW evacuation, 609
supply, October includes 50 supply.
So the digest title is clear, it is counting sorties by heavy bombers,
regardless of the mission type.
Bomb tonnages do not agree as well as the sorties, month, duty
sheets (effective plus jettisoned bombs), digest,
Jan-44 \\ 10,855 \\ 11,051
Feb-44 \\ 6,548 \\ 6,747
Mar-44 \\ 10,264 \\ 10,376
Apr-44 \\ 21,210 \\ 21,256
May-44 \\ 30,236 \\ 30,355
Jun-44 \\ 25,131 \\ 24,466
Jul-44 \\ 29,799 \\ 32,183
Aug-44 \\ 27,976 \\ 27,839
Sep-44 \\ 20,782 \\ 20,856
Oct-44 \\ 16,162. \\ 16,257
So the digest is counting jettisoned tonnage.
The target and duty sheets often record the altitude the bombs
were released at, the maximum was 32,000 feet by a B-17 group,
the highest recorded B-24 altitude was 27,000 feet, it is the only
B-24 entry of 26,000 feet or higher, versus the 120 B-17 entries.
Lowest bombing altitude, assuming no mistaken entries, was
2,300 feet, then one at 3,500 feet, all other entries are 11,000
feet or higher.
The target and duty sheets note fighters escorting early
returning bombers were classified as being Non Effective sorties,
thereby increasing the "headline" unreliability rate for fighters.
15th Air Force P-38 units dropped over 3,000 tons of bombs, the
P-47 units none and the P-51 units 1 ton in April 1945.
Some of the 1945 monthly reports have Engine Change Reports,
graphs of average running time per aircraft engine changed.
Generally speaking the R-1830 radials in the B-24 and the R-1820
radials in the B-17 had at least an average of 300 hours running when
changed, few had 400, with the R-1820 ahead, most having 350 or
more hours. Overhauled engines usually had around half the average
hours of new engines. The V-1650 Merlins and the V-1710 Allisons
usually averaged over 200 hours, few made it to 300 until March/April.
Overhauled Allisons were around half the new engine hours, overhauled
Merlins more like a quarter.
Geoffrey Sinclair
Remove the nb for email.
The 15th Air Force was officially formed on 1 November 1943,
with 4 B-17, 2 B-24, 1 B-25 and 3 B-26 groups. The B-25
group was reassigned to the 12th Air Force on 3 November, the
B-26 groups on 1 January 1944. For fighter cover there were
3 P-38 and 1 P-47 groups.
Final strength was 6 B-17 and 15 B-24 groups, along with 3
P-38 and 4 P-51 groups, with the 332nd fighter group having
4 squadrons of P-51s instead of the normal 3.
No new units became operational in 1943, two new B-24
groups flew their first mission on 8 January 1944, another on
the 30th, February saw three more B-24 groups flying their
first missions on the 8th, 10th and 12th, March had 1 new
B-17 group (on the 30th) and 2 B-24 groups, on the 2nd and
19th, four new groups in April, a B-17 on the 12th and 3 B-24
on the 2nd, 29th and 30th, finally in May 2 new B-24 groups
flew their first missions on the 5th and 10th.
A P-51 group was transferred from the 12th Air Force and
flew what is reported to be the first P-51 operation in the
Mediterranean as its first 15th Air Force mission on 16
April. Another P-51 group was transferred from the 12th
and flew its first 15th Air Force mission on the 10th of May.
The original P-47 group, the 325th, converted to P-51 in
May 1944, last P-47 operations on the 24th, first P-51 on
the 27th. Finally the 332nd fighter group was transferred
to the 15th Air Force while it was converting from the P-39
to the P-47, it flew P-47 operations from 7 to 30 June while
converting to P-51s, with the first P-51 operation on 4 July.
It is clear that in mid May 1944 the 15th Air Force had a real
fighter shortage, 21 bomb to 6 fighter groups, finally ending
up with 7 fighter groups.
At the other end of the campaign, 2 B-24 groups were
returned to the US in mid April 1945, while by the end of
May 1945 another 4 B-24 groups had been returned to
the US and another 4 assigned to Air Transport Command
in Natal, Trinidad and Casablanca. Planning as of the
end of May 1945 was that only 3 of the original B-17 groups,
the 2nd, 97th and 99th, would remain in Europe, the rest of
the bomb groups would be returned to the US by end July,
followed by the fighter groups.
This follows the pattern in the 8th Air Force, the rapid
retirement of the B-24 while retaining the B-17.
Overall the B-17 accounts for 31.5% of all airborne 15th Air
Force heavy bomber sorties, but 32.5% of effective sorties,
that is they completed the mission. As with the 8th Air Force
a number of airborne sorties were spares to replace any
aborting aircraft, unused spares were classified along with
any early aborts as Early Return, or Non Sorties, the B-17
accounts for 32.4% of such sorties. The B-17 accounts for
28.5% of aborts due to weather, 26.1% due to mechanical
problems, 22.7% for aircraft and accessory problems, 19%
for lead ship failure (radar bombing) but 38.7% of
miscellaneous reason aborts, overall 19.9% of B-17 and
23.3% of B-24 sorties were non effective.
Clearly the number of early returns is influenced by the number
of spare sorties and the number of lead ship failures by the
amount of radar bombing, but overall it is seen the B-17 was
the more reliable. In addition overall around 77% of B-17 were
operational at any one time versus 69% of B-24s.
Weather aborts are broken down into two categories, target
obscured and failed to reach target. From January 1944 on
8,664 fighter and bomber sorties found the target obscured,
12,380 failed to reach the target.
The 15th Air Force first used H2X to aim bombs on 15 April
1944, against Bucharest, and unfortunately the different
references disagree about what attacks used H2X. As the
analysis currently stands from 15 April to end October 1944
there were 2,988 effective B-17 and 3,764 effective B-24
sorties using H2X, plus 8 B-17 and 3 B-24 effective sorties
using H2X at night. For the remainder of the war there are
around another 20,000 day and 150 night effective sorties
using H2X.
When it comes to losses the B-17 was 32.2% of heavy bombers
reported lost to enemy aircraft, 23.3% to flak, 25% to mechanical
or other reasons, and 26.6% of unknown cause losses. As a
percentage of effective sorties, B-17 loss rate was 1.5%, the
B-24 2%. The B-17 had 34.2% of heavy bomber encounters
with enemy aircraft, that is 4,531 versus 8,703 for the B-24. So
overall it appears to have been slightly less vulnerable to fighter
attack and definitely less vulnerable to flak and equipment failure,
but as "unknown cause" makes up 14.7% of reported losses the
results have a significant error margin.
For every bomber lost on operations another 5.25 were listed
as damaged, for the B-17 it was 6.9 damaged to destroyed,
for the B-24 5.1 to 1, implying the B-24 took less damage to
shoot down or was being systematically sent to more lightly
protected targets. There seems to be a bias at times to use
higher flying B-17 units on heavily defended targets, but how
much this matters over the course of the campaign is another
matter.
However the large number of sorties to mainly communication
targets in Italy disguises the loss rates, both oil and industry
targets, mainly outside Italy, had an aircraft loss rate of 3.1%.
The personnel loss records have 3.8% of casualties in the
Adriatic, which could mean from missions against a number of
countries, plus 5% of casualties to "other countries", in both
cases bomb tonnage dropped is zero. With that in mind targets
in Austria are reported as having been attacked by 24% of bombs
dropped and resulted in 24.2% of casualties (killed, wounded,
missing, PoW), Germany 11.6% of bombs, 14.1% of casualties,
Romania 8.5% of bombs, 9.8% of casualties, Italy 29.4% of
bombs, 18.2% of casualties and surprisingly Yugoslavia with
7.1% of bombs but 12.9% of casualties.
Accidents on non operational sorties lost 43 B-17 and 192 B-24.
The 15th Air Force uses destroyed and missing categories for
aircraft losses on operational missions, it is clear most destroyed
aircraft would be classified as missing in the system used by
the 8th Air Force, so no comparison is possible when it comes to
aircraft that returned to friendly territory too damaged to be repaired
versus those lost over enemy territory.
Unfortunately while there are figures for the total number of
sorties by B-17 and B-24 for the campaign so far no official
campaign total of bomb tonnage by aircraft type has been found.
Monthly figures for bomb tonnage by type are available from
January 1944 on but not sorties by type. In addition some key
reports use pilot sorties which are all sorties that crossed
enemy lines, whether effective or not, which means they
cannot be used to calculate bombs dropped per effective sortie.
The B-17 dropped 104,877 tons of bombs January 1944 onwards,
the B-24 192,113 tons, B-17 effective sorties from November
1943 onwards are 41,751, B-24 86,838. Even with the missing
bomb tonnage it is clear the B-17 was carrying the heavier loads
on average.
To obtain an idea on average bomb loads the data in the "Target
and Duty Sheets", which give a break down by bomb group, have
been used even though they are only available for the December
1943 to October 1944 period at the moment and the December
1943 figures do not include tonnage classified as jettisoned.
For effective B-17 sorties December 1943 to October 1944 the
average bomb load dropped was 5,400 pounds, for B-24 it was
4,690 pounds. These figures are a slight underestimate, as
some sorties classified as effective have at least some of
their bomb tonnage classified as jettisoned.
On an administrative note the number of effective sorties used in
the above calculation excludes 58 B-17 PoW evacuation sorties
in August and September 1944 and 659 B-24 supply mission
sorties to France in September and October 1944 as well as
a small number of reconnaissance and air sea rescue sorties.
The jettisoned bomb tonnage listed in the Target and Duty
Sheets is significant, for January to October 1944 it is 16,777
tons versus 182,185.6 tons dropped by effective sorties. Most
jettisoned tonnage is that, but some appears to be bombs
that for example hung up but later dropped or were dropped
clear of any recognised target, "unaimed" bombs perhaps.
As a sanity check the results can be compared with the USAAF
Statistical Digest figures, firstly for airborne heavy bomber sorties
in the Mediterranean theatre, month, duty sheets, digest,
Jan-44 \\ 4778 \\ 4,720
Feb-44 \\ 3974 \\ 3,981
Mar-44 \\ 5997 \\ 5,996
Apr-44 \\ 10171 \\ 10,182
May-44 \\ 14425 \\ 14,432
Jun-44 \\ 11737 \\ 11,761
Jul-44 \\ 12656 \\ 12,642
Aug-44 \\ 12197 \\ 12,194
Sep-44 \\ 10081 \\ 10,056
Oct-44 \\ 9645 \\ 9,567
January sorties include 11 Air Sea Rescue, March include 1 weather
reconnaissance, July include 7 photo reconnaissance, August include
4 photographic reconnaissance, 1 special mission, 1 secret mission,
38 PoW evacuation, September include 20 PoW evacuation, 609
supply, October includes 50 supply.
So the digest title is clear, it is counting sorties by heavy bombers,
regardless of the mission type.
Bomb tonnages do not agree as well as the sorties, month, duty
sheets (effective plus jettisoned bombs), digest,
Jan-44 \\ 10,855 \\ 11,051
Feb-44 \\ 6,548 \\ 6,747
Mar-44 \\ 10,264 \\ 10,376
Apr-44 \\ 21,210 \\ 21,256
May-44 \\ 30,236 \\ 30,355
Jun-44 \\ 25,131 \\ 24,466
Jul-44 \\ 29,799 \\ 32,183
Aug-44 \\ 27,976 \\ 27,839
Sep-44 \\ 20,782 \\ 20,856
Oct-44 \\ 16,162. \\ 16,257
So the digest is counting jettisoned tonnage.
The target and duty sheets often record the altitude the bombs
were released at, the maximum was 32,000 feet by a B-17 group,
the highest recorded B-24 altitude was 27,000 feet, it is the only
B-24 entry of 26,000 feet or higher, versus the 120 B-17 entries.
Lowest bombing altitude, assuming no mistaken entries, was
2,300 feet, then one at 3,500 feet, all other entries are 11,000
feet or higher.
The target and duty sheets note fighters escorting early
returning bombers were classified as being Non Effective sorties,
thereby increasing the "headline" unreliability rate for fighters.
15th Air Force P-38 units dropped over 3,000 tons of bombs, the
P-47 units none and the P-51 units 1 ton in April 1945.
Some of the 1945 monthly reports have Engine Change Reports,
graphs of average running time per aircraft engine changed.
Generally speaking the R-1830 radials in the B-24 and the R-1820
radials in the B-17 had at least an average of 300 hours running when
changed, few had 400, with the R-1820 ahead, most having 350 or
more hours. Overhauled engines usually had around half the average
hours of new engines. The V-1650 Merlins and the V-1710 Allisons
usually averaged over 200 hours, few made it to 300 until March/April.
Overhauled Allisons were around half the new engine hours, overhauled
Merlins more like a quarter.
Geoffrey Sinclair
Remove the nb for email.