History of Global Arms Transfer, 18 (2024), pp. 45-61

In Consideration of Nighttime Precision
Bombing by the U.S. during World War II:
Its Historical Significance andFuture Tasks
By SATOSHI FUJITA*This article focuses on the nighttime precision bombing campaign using a latest
radar conducted by the United States Army Air Forces at the end of World War II.
Previous studies have paid little attention to this campaign, which lasted from lateJune 1945 until the end of the war. This article shows that it has historicalsignificance in that the mobilization of science, technology, and industry madepossible certain tactics that were previously considered unfeasible. This campaign
also suggests that the state of science, technology, and industrial policies
determined the way the war was fought. This paper presents the future tasks
whose completion is necessary to illuminate the overall picture of the campaign.
First, it is necessary to clarify how the scientific, technological, and industrial
bases that enabled these tactics were put in place and, second, to elucidate why
oil-related facilities were selected as targets for nighttime precision bombing
operations. By answering these questions, we will be able to offer a fullperspective of nighttime precision bombing operations with the radar and, byextension, understand the characteristics of how the American military fought thewar.

Introduction
This article discusses the strategic bombing campaign against Japan conducted by theUnited States Army Air Forces (USAAF) in the final months of World War II. Particularly,
it focuses on the nighttime precision bombings of petroleum facilities beginning in lateJune 1945, summarizes these operations and results, examines their strategic impacts andhistorical implications, and clarifies future tasks that should be accomplished.
To offer an early conclusion, the operations against petroleum facilities had little
influence on the consequences of the war. Therefore, previous studies have only referenced
them briefly, if ever, and they failed to examine their historical significance1. Although theofficial history of the 315th Bombardment Wing details the personnel, training, and* Author’s Affiliation: Satoshi Fujita, Associate Professor, Department of International Communication, Gifu
City Women’s College.
1 Craven and Cate [1983b:1955]; United States Air Force [1953]; Werrell [1996]; Crane [2016]. The latest
study of the history of the U.S. precision attacks and strategies does not refer to this campaign at all. Rogers[2023].

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SATOSHI FUJITA
missions of the unit (information on which this article depends heavily), this study does notdetail any industrial, scientific, or technological bases that could elucidate their operations,and it fails to identify their historical implications2.
However, these operations did have historical implications in that they demonstrated theimportance of science and technology, as operations previously considered unfeasible weremade possible with the newly developed radar. In addition, to perform the operation
required not only technological developments but also a certain amount of equipment to be
produced, that is, industrial mobilization. As historian Paul Kennedy suggests, thefeasibility of certain tactics or operations depends on scientific and technological efforts,
and identifying them is important, despite tending to be underestimated3. Indeed, theperformance and success of the nighttime precision bombing depended on many factors.
That is, exaggeratedly, to paint a complete picture of these operations reveals how the US
fought the war.
Concerning the American way of war, especially strategic bombing during World War II,
most previous studies focus on the transition from precision tactics to indiscriminate ones.
Quoting Paul Fussell’s literature, Eiko Ikui points out that the US military placed value on
accuracy in the early stages of the war, but in the latter phase, accuracy and precision was
not considered important and the way of fighting changed to one that prioritized efficiency
and consumed large amount of munitions 4. Some authors accuse the US military of
performing strategic, especially indiscriminate bombing as immoral act5. For them, the US
and the Great Britain (also Germany and Japan) violated international laws stipulating thatany military had not to target innocent civilians. By reflecting the strategic bombing
campaign during World War II from this perspective, however, such authors dismiss the
US’ efforts to pursue a precision attack as a way of more economical and humanitariantactics. After World War II, the US military have continued to do so. As James Patton
Rogers suggests, analyzing the American pursuit of precision “reveals rare insights into theintellectual history, evolution, and character of American warfare6.” Therefore, this article
sheds light into the American way of war by examining previously overlooked operations
during World War II.

1. Summary of the Strategic Bombing of the Japanese Homeland
To place in a context the nighttime precision bombing during the last stage of World War
II, this chapter summarizes the strategic bombing campaign against Japan. First, what is a“strategic bombing”? Attacking an enemy from the air is generally defined as two methods.
One is “tactical,” to support a fighting on the front line, and it involves targeting enemy
forces themself, as well as the roads, railroads, and bridges used to transport personnel andsupply. Although roads, railroads, and bridges are the targets of “strategic bombings,” theaim of a tactical attack is to support ground forces.
The second method is strategic, aiming to diminish the enemy’s war-fighting ability. In
modern wars, especially in total wars, which are fought with all the strength of a nation,
2 Swann [1986].
3 Kennedy [2013].
4 Ikui [2018: 2006] pp. 168-179. See also Schaffer [1985].
5 See Grayling [2006] and Arai [2008].
6 Rogers [2023] p. 2. As mentioned above, however, Rogers does not refer the nighttime precision bombing

campaign with a radar during World War II.

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In Consideration of Nighttime Precision Bombing by the U.S. during World War II
continuation of the war requires industrial productivity to supply munitions and labor
forces to support the productive capability. Therefore, the desirable targets for strategic
bombings are as follows: military arsenals, powerhouses, fuel factories, cities, andcivilians. Bombing cities also has the purpose of demoralizing the civilian population toraise war weariness among them, leading to a quick end to the war.
Furthermore, strategic bombing consists of two methods: precision bombing and area
bombing, where the former aims for the targets mentioned above accurately and withminimum bombers, bombs, and sacrifices of enemy civilian. As detailed later (3-1), theUSAAF preferred this method of bombing from an economic and humanitarian perspective,
but it is technically difficult to pinpoint a target with bombs from the air. Meanwhile, area
bombings target objectives and the surrounding neighborhood, destroying them certainly.
This means area bombings produce greater civilian losses and they are indeed applied todestroy a city itself and kill its civilians as a demoralization tactic.
In both European and Pacific theaters, because the Allies could attack the German andJapanese homelands only by bombing from the air, strategic bombing garnered high hopefrom the war’s onset. It was reflected by the fact that while the US produced about 300,000
aircrafts during the war, it weighed long-range bombers, such as B-17s, B-24s, and B-29s
used primarily for strategic bombing7. Among these, B-29s were the latest and most longrange, so they were most appropriate for attacking Japan proper. The Twentieth Air Force(20th AF) was responsible for bombing Japan, and all heavy bombers received by the 20th
AF were B-29s. During the war, approximately 3,700 B-29s were produced, and over 1,000
among them were delivered to the 20th AF8.
As such, the 20th AF was organized to perform strategic bombing against Japan. The war
against Japan had many theaters, including China-Burma, the Pacific, the Far East, andAlaska, and Air Forces were deployed to each. This meant that each Air Force was subject
to the policies of the commanding general of each theater. In contrast, the 20th AF wassolely responsible for the Joint Chiefs of Staff, the top military decision maker, and they
could then engage in the bombing of Japan, regardless the policy of each theater. Further,the 20th AF had two bomber commands (BC), the 20th and 21st, the former of whichplaced its headquarters at Kharagpur, India, and conducted a bombing campaign against
Japan, East Asia, and Southeast Asia as a whole from forward bases, such as Chengdu,
China. In addition, the 21st BC, based on the Mariana Islands, which were conquered inJuly and August 1944, carried out a bombing campaign against the Japanese homeland. As
chief portions of the 20th BC were incorporated into the 21st BC later, this article examines
mainly the actions of the 21st BC.
The 21st BC consisted of five bombardment wings (BW): the 73rd, 313th, 314th, 58th,
and 315th Wings, in order of deployment to Marianas. Each BW comprised four
bombardment groups (BG), and each BG was authorized to have 45 B-29s, totaling amaximum BW force of 180 B-29s. However, each BW or BG began operating before theirforce was complete, and the build-up of each force advanced gradually9.
The commander of the 21st BC was Haywood Hansell, Jr., who was an enthusiastic
advocate of “precision” bombing10. Because the Japanese aircraft industry was set as the
7 Approximately 35,000 long-range bombers were produced during the war. The total airframe weight of longrange bombers was 35% of that of all aircrafts built by the war’s end. Craven and Cate [1983c:1955] pp. 352–
353.
8 Muelen [1995]; Office of Statistical Control [1945] p. 179.
9 Craven and Cate [1983b] p. 522.
10 Haun [2019] p. 220.

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SATOSHI FUJITA
primary target at the headquarters of the 20th AF, the 21st BC engaged primarily in
precision bombing against the installations relating to the aircraft industry in the first phaseof the campaign. On November 24, 1944, 21st BC ushered its first operation with 111
B-29s against the Nakajima Aircraft Musashi plant. This operation, however, could not
produce a significant result, so the Musashi plant was attacked repeatedly. Three days later,
the 21st BC targeted Musashi plant again, but no airplane could drop bombs on the primaryobjective. Due to heavy clouds, the units could not conduct visual, that is precision,
bombing, so they dropped their bombs on an urban area set as the secondary target of themission. Many similar cases were seen. For example, the original target of the Ginza air
raid on January 27, 1945, was the Musashi plant. These facts represent the reality of“precision” bombing campaigns11.
The 21st BC changed its policy clearly in late February 1945, and in January 1945,
Hansell was replaced by Curtis LeMay as head of the 21st BC. The headquarters at
Washington hoped that LeMay would make a difference through massive incendiary attacks
on large cities, instead improving “precision” bombing. However, LeMay did not begin thearea bombing operation using incendiaries immediately upon his arrival as the commander.
While he “tested” the incendiary bombing against cities twice, he waited for the number of
B-29s necessary to conduct such an operation to be deployed and readied. On February 25,
his “test” had achieved success with 229 B-29s, so he decided to conduct a full-scale
operation against Tokyo12. Thus, 325 B-29s took off from Mariana Islands toward Tokyo on
the night of March 9, dropping their bombs at midnight from a low altitude (about 9,000ft), and their bodies were made lighter by removing their arms so they could carry more
incendiaries. The extent of the damage caused by this operation has been well documented.
Beginning with the Tokyo air raid, the 21st BC conducted successive operations against
urban areas of large Japanese cities: Nagoya, Osaka, Kobe, and again Nagoya. However,the 21st BC involved not only the incendiary campaign, but also some additional
operations. First, the Command engaged in a “tactical” bombing of the Kyushu airfields as
a part of the Okinawa campaign, which began in April 1945 and continued to the middle of
May13. Second, the 313th BW assumed the mining campaign on Japan Sea, Inland Sea, andmore from late March, and it was continued until the war was over. The official history of
the USAAF during the World War II, The Army Air Forces in World War II (hereafter, AAF
in WW II), described that the mining campaign had achieved meaningful results14.
Concerning the incendiary bombings of large cities, the 21st BC targeted the Nagoya
urban area on March 18 and Kawasaki and Tokyo on April 15. After an interval of about amonth, the 21st BC resumed the campaign with raids against Nagoya on May 14 and 17. A
month after that, the incendiary campaign against “large” cities ended with attacks on
Osaka and Amagasaki, flying 511 superforts15. Since then, the 21st BC aimed at middle orsmaller cities populated from 31,350 (Tsuruga) to 323,200 (Fukuoka) with incendiaries
until the war ended16. While attacks against large cities were conducted by almost all forces
available to the Command (300–500 B-29s), middle or smaller cities were bombed by one
bombardment wing (100–180 B-29s). Until the war ended, over 60 cities had been burnedout.
11 Koyama [2018] pp. 29–30.
12 Fujita [2021].
13 Craven and Cate [1983b] pp. 627–635.
14 Craven and Cate [1983b] pp. 662–674.
15 Craven and Cate [1983b] pp. 608–627, 635–644.
16 Craven and Cate [1983b] pp. 653–658, 674–675.

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In Consideration of Nighttime Precision Bombing by the U.S. during World War II
Despite LeMay’s policy change, precision bombing of war industries, such as aircraft
plants, was not abandoned, and this kind of operation was conducted repeatedly over
several months. For example, the 21st BC engaged in precision bombing operations against
the Musashi plant and Tokyo Army arsenal on August 8, Ogikubo plant of Nakajima andTokyo Army arsenal again on August 10, and Hikari Navy arsenal (Yamaguchi) and Osaka
Army arsenal on August 14. LeMay modified the operational method, such as lowering
bombing altitude and using far heavier bombs to achieve far more meaningful results thanHansell’s operations17.
As stated above, 21st BC involved many kinds of bombing operation since LeMay had
assumed the role of commander. This was possible because personnel and aircrafts were
deployed one after the other to the Mariana Islands, and readied to begin these missions.
The 313th BW, a second unit that arrived at Marianas, began its operation on February 4,1945. In addition, the 314th BW joined the “test” incendiary attack against Tokyo on
February 25, leading to the air raid on March 9 conducted by three BWs. Nighttime
precision bombings with a newly developed radar against oil facilities by the 315th BW
were carried out in the context of building forces and diversifying operations. The next
chapter describes in detail all the operations of the 315th BW based on AAF in WWII, A
Unit History of 315 Bomb Wing: 1944-1946, and the documents of the United States
Strategic Bombing Survey (USSBS)18.

2. Missions of the 315th Bombardment Wing
The 315th BW, activated on July 17, 1944, was deployed incrementally from March to
April 1945, having received B-29Bs, a variant of the B-29 dedicated to nighttime
operations and equipped with a new radar device, the AN/APQ-7, to carry out nighttime
precision bombings of oil facilities. The BW consisted of four bombardment groups, the16th, 501st, 331st, and 502nd, in order of deployment at Marianas. The 16th and 501st BGs
conducted their first operations on June 26 and the 331st and 502nd on July 19. It took
about a year from the activation of the BW to the beginning of actual operations, indicatingthat engaging required various preparations, including the deployment of B-29s, theconstruction of bases, and training. These issues will be discussed in another paper.
Table 1 shows all missions by the 315th BW, that is, 15 missions aimed at 9 targets. Totalsorties were about 1,200 and total weight of bombs dropped was 9,084 tons. Bomb weight
per one aircraft was relatively heavy due to using B-29Bs, which were deprived of mostarming to conduct nighttime bombings. Their first mission targeted Utsube River Oil
Refinery (Second Navy Fuel Arsenal, Yokkaichi, Mie), with 35 bombers of the 16th and502nd BGs and dropping 223 tons. The damage of this mission on its own was unclear, but
combined with the damages of mission number 209 on June 17, which attacked Yokkaichi
city, issuing collateral damage to this oil refinery, and mission number 218 on June 22,
which aimed it for a secondary target, the 315th BW’s first mission destroyed 34% of theroof area and rendered 1.6% of the oil capacity (33,870/2,073,080 barrels) unavailable.
This target was bombed on July 9 again, and because of all these missions, half the roof
area was destroyed and 4% of the oil capacity was rendered unavailable (according to
17 Craven and Cate [1983b] pp. 646–653.
18 The USSBS documents used in this article are mainly Damage Assessment Reports. All have been collectedby the National Diet Library, Japan. Its Digital Collection is made almost entirely available (https://dl.ndl.go.jp/
collections/A00018).

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SATOSHI FUJITA
Table 1. All Missions by the 315th Bombardment Wing
Date of Mission(Mission Number)Primary Target

SortiesNumber of B-29s which
dropped bombs against
primary target

Weight of
Bombs
Dropped (tons)

June 26（232）

Utsube River Oil Refinery(Yokkaichi)

35

33

223

June 29（238）

Nippon Sekiyu Oil Refinery(Kudamatsu)

36

32

209

July 2（245）Maruzen Oil Refinery (Shimotsu)

40

39

297

July 6（255）

Same as above

60

59

442

July 9（261）Same as number 232

64

61

469

July 12（267）

Kawasaki Petroleum Center

62

55

452

July 15（270）Same as number 238

71

61

494

July 19（281）

Nippon Oil Refinery (Amagasaki)

86

85

702

July 22（283）

Ube Coal Liquefaction Co.

82

74

637

July 25（291）

Mitsubishi Oil Refinery and Hayama
Petroleum Company (Kawasaki)

85

77

668

July 28（303）

Shimotsu Oil Refinery

84

78

658

August 1（310）Same as number 267

130

121

1,025

August 5（315）Same as number 283

113

108

938

August 9（322）Same as number 281

109

97

918

143

134

954

August 14（328） Nippon Oil Refinery (Tsuchizaki)

Source: Koyama [2018]. There are some cases in which the number of sorties and the weights of the bombs
dropped differ from those mentioned in the text.

Damage Assessment Report 141, 41.6% of the capacity had been “removed” before theattacks, but in the reports, the amount “removed” was counted as “damage”)19.
The second target was Nippon Sekiyu Oil Refinery (Kudamatsu, Yamaguchi), attacked onJune 29 and July 15, and these missions rendered 60% of the oil capacity (349,000/58,7000
barrels) unavailable20. Then, on July 2 and 6, Maruzen Oil Refinery (Shimotsu, Wakayama)
was attacked by the 315th BW. Like earlier missions, the first of two made a trivial
difference, but the latter destroyed 79% of the roof area. Total tank damages showed that
51.5% was classified as “destroyed” and 37% as “damaged” (total tank capacity was about
a million barrels)21. Curtis LeMay described the latter mission as the most successful radarbombing ever 22, foreshadowing the overall success of nighttime precision bombing
campaigns with the most advanced radar.
19 Damage Assessment Report, no. 141, mission 261 (July 9–10) combined with 209 (June 18), 218 (June 22),and 232 (June 26), July 17, 1945.
20 Damage Assessment Report, no. 179, mission 270 (July 15–16), combined with 238 (June 29), August 15,
1945.
21 Damage Assessment Report, no. 142 mission 245 (July 2) and 255 (July 6), July 21, 1945.
22 Werrell [1996] pp. 199–200.

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In Consideration of Nighttime Precision Bombing by the U.S. during World War II
The next target was Kawasaki Petroleum Center, a complex of Standard Vacuum Oil Co.,
Nippon Oil Co., Mitsui & Co., and Rising Sun Petroleum Co., toward which 60 B-29s flew,
53 of which dropped 452 tons on the primary target. However, this attack destroyed ordamaged only 6% of tank capacity (total 1,334,000 barrels) 23. On July 19, the operation
against Nippon Oil Refinery (Amagasaki) produced “excellent results,” according to a
mission resume 24, and the Amagasaki plant was bombed again on August 9, with theDamage Assessment Report (no. 191) recording the total damage of these missions at about
70% of the original total oil capacity (1,175,400/1,496,700 barrels) 25.
Ube Coal Liquefaction Co., “the largest synthetic oil producer in the Japanese inner zone
outside Manchuria,” was the next target of 80 airborne aircraft, 90% of which dropped 620
tons on the primary target26. Although the results of this mission itself are unclear, the strikeattack report of this operation noted that “excellent results are indicated by scope photos27.”
On August 5, the 315th BW carried out a second raid against Ube plant that resulted in“100% of refinery units and 80% of the stores and workshops damaged or destroyed28.”
According to the Damage Assessment Report (no. 175), the combined results of the 315th
BW’s missions (54.5%) with previous removal (45.5%), the plant became completely
inoperative29.
On July 25, the 315th BW attacked Kawasaki, an operation to which two additionalbomber groups joined. Many targets were bombed, including Mitsubishi Oil Refinery and
Hayama Petroleum Company, toward which 83 B-29s flew, 75 of which dropped 650 tons
on the primary targets30. In addition, on August 1, Kawasaki Petroleum Center was bombedagain with 1,017 tons by 120 B-29s (of 128 airborne). According to the damage assessment
reports, the combined results of these missions are as follows: 537,400 barrels, 38% of
Mitsubishi’s original capacity (1,404,400 barrels) was damaged or destroyed; 334,000
barrels of 761,600 barrels at Hayama plant was rendered unavailable; and half of Kawasaki
Petroleum Center’s tank capacity, all combined with the damage by the mission in midJuly31. Between bombings of Kawasaki, on July 28, the 315th BW attacked Shimotsu Oil
Refinery (different from Maruzen Oil Refinery) and damaged and destroyed 75% of thetotal capacity (927,300/1,246,000 barrels)32.
The last target of the 315th BW was Nippon Oil Refinery, located in Tsuchizaki, Akita
prefecture. This mission was the “longest and largest raid of the war” by 315th 33,
considered generally successful, as 70% of the original capacity was destroyed anddamaged, and “[t]he buildings of the refinery were 98% affected, 87% destroyed and 11%
23 Damage Assessment Report, no. 157, mission 267 (July 12–13), August 3, 1945.
24 Mission Resume for mission 251 (July 19–20). The damage assessment report for this mission recorded thedamage of the attack as 39% of tank capacity (587,300/1,496700 barrels). The history of the 315th BW, however,notes, “Post-mission photo-reconnaissance showed the wing mission on Amagasaki had mixed results.” Swann[1986] p. 102.
25 Damage Assessment Report, no. 191, mission 322 (August 9–10), August 21, 1945.
26 Target Information Sheet, Ube Coal Liquefaction Company, July 20, 1945.
27 Strike Attack Report, no. 130, mission 283 (July 22–23), July 27, 1945.
28 Mission Resume for mission 251 (August 5–6). This attack also damaged or destroyed half of the Ube Iron
Works Co.
29 Damage Assessment Report, no. 175, missions 270 (July 15–16), 283 (July 22–23), and 315 (August 5–6),
August 14, 1945.
30 Mission Resume for mission 291 (July 25–26), August 3, 1945.
31 Damage Assessment Report, no. 173, missions 291 (July 25–26) and 310 (August 1–2), August 10, 1945;
Damage Assessment Report, no. 184, mission 310, August 18, 1945.
32 Damage Assessment Report, no. 172, mission 303 (July 28–29), August 12, 1945.
33 Swann [1986] p. 113.

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SATOSHI FUJITA
gutted and seriously damaged34.” On the same day, when the Japanese government decided
to surrender, the 20th AF carried out full-fledged attacks on various targets with over 800
B-29s. The commanding general of the USAAF, Henry Arnold, hoped “as big a finale apossible” against Tokyo; he planned to call on the Eighth Air Force, a part of which had
been transferred to Okinawa from Europe35. However, his subordinate, Carl Spaatz, argued
that Tokyo was not appropriate for such an operation and proposed to attack various targets,
which Arnold accepted36. As such, the 315th BW completed their mission as usual.
Concerning the achievement of 315th BW, AAF in WW II concluded:
On the whole, the experiment was markedly successful. The formations were able toattack the primary target on every mission, and while the results varied they weregenerally good… USSBS statisticians calculated that 315th Wing bombardiers had
achieved an accuracy rate of 13.5 per cent, as compared with 5.4 per cent achieved,
under more difficult tactical conditions, with the Eagle [AN/APQ-7] radar in Europe37.
Moreover, as with the accuracy of the campaign with the AN/APQ-7, military historian
Kenneth P. Werrell states, “Eagle demonstrated accuracy approximating that of visual
bombing, and on occasion exceeding it38.” The accuracy of the 315th BW’s missions
depended on many factors, so it should not be attributed only to the performance of the
EAGLE radar39. However, LeMay was overly impressed by the achievement of the unit, so
he planned to change the targets of the 315th from oil to nitrogen plants and bridges and to
install the EAGLE radar in the B-29s of the other wings40.

3. Some issues of nighttime precision bombing
In this chapter, the author describes three issues of nighttime precision bombing, the first ofwhich is the USAAF’s strategic bombing doctrine. Second, it is important to identify how
this kind of campaign was made possible and, third, why oil-related facilities were targeted.
3-1. Strategic Bombing Doctrine of the USAAF
The purposes of strategic bombing are, as noted in Chapter 1, destruction of the enemy’s
war capacity by attacking directly the political and industrial core and by demoralizing the
population through targeting non-combatants. Then, precision bombing and area bombing
were assumed as means to accomplish these ends. Precision bombing literally means
dropping bombs on a target, such as a war plant, “precisely,” whereas with area bombing,bombers attack the surrounding “area” of a target. Because the method also hurts thecivilian of the area attacked, it is used to target non-combatants directly.
34 Damage Assessment Report, no. 205, mission 328 (August 14–15), September 10, 1945.
35 Maurer [1983b] p. 463.
36 Craven and Cate [1983b] p. 732.
37 Craven and Cate [1983b] p. 661.
38 Werrell [1996] p. 200.
39 The United States Strategic Bombing Survey, Oil and Chemical Division, Oil in Japan’s War, pp. 121–123,

National Diet Library Digital Collection. This report lists factors that led to differences in accuracy between theEuropean and Pacific theaters (315th missions), including bombing altitude, opposition violence, and bomb size.
In the European theater, altitude was higher, opposition was more violent, and bombs were lighter than in the
Pacific.
40 Werrell [1996] p. 200.

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In Consideration of Nighttime Precision Bombing by the U.S. during World War II
Within the US Army, the Air Corps Tactical School (ACTS), which was originallyestablished as the Air Service Tactical School in 1920, studied the doctrine of strategic
bombing. This group was called the “Bomber Mafia,” one of whom was Haywood Hansell.
They established precision bombing as their doctrine, as well as put forth the “Industrial
Web Theory,” which assumes that the various parts of a modern city are connected to andinteract with each other complicatedly like a “web.” Therefore, they considered thedestruction of one important part of a city enough to spread the effect throughout, and they
thought it was technically possible to bomb precisely thanks to the new availability of
B-17, the then-newest long-range bomber, and the Norden bombsight by the middle of the
1930s41.
Moreover, the international law and the moral of a bombing from the air was took into
consideration. In an interwar period, although any treaty that prohibits the bombing ofcivilian was not realized, major powers discussed whether or not it was justified, resulting
in Hague Rules of Air Warfare (1923) that stipulates that “Aerial bombardment for the
purpose of terrorizing the civilian population, of destroying or damaging private property
not of military character, or of injuring non-combatants is prohibited42.” As Arai Shin’ichi
suggests, this Rules functioned as the guides for air warfare of many states43. In particular,
the US government disliked the bombing of civilian from moral perspective. Henry L.
Stimson, then-secretary of state, strongly condemned Japan for bombing of urban arears ofChinchow and Shanghai during the Manchurian Incident, and the President Frankin D.
Roosevelt, in 1939, demanded the belligerent nations not to “undertake the bombardmentfrom the air of civilian populations of unfortified cities…44” Against this backdrop, theACTS developed precision bombing doctrine45.
In a sense, World War II was a spectacular testing site for demonstrating that the strategic
bombing doctrine of the USAAF would work well. Then, both in Europe and the AsiaPacific theater, it became apparent that the doctrine was only theoretical and ideal.
Although the USAAF engaged strategic bombing operations with the Royal Air Force(RAF) in Europe, US precision bombing, that is, daytime visual bombing from a highaltitude, was not only safe but also precise. The RAF, which was involved in strategic
bombing against Nazi Germany from an earlier stage of the war, had already changed thepolicy from precision to nighttime area bombing using a radar46. The USAAF, however,
was adamant that its original method was superior. However, in the daytime, bombers weresusceptible to enemy intercepts, and from a high altitude, crews could not drop bombs ontargets precisely. Although the USAAF continued precision bombing only officially, it
launched de facto area bombing with an attack against Münster in October 1943—thisresulted in the Dresden bombing in February 194547.
Daytime visual bombing from a high altitude, which had not worked in Europe, wasapplied in the war against Japan for certain reasons. First, the headquarters in Washington
set the Japanese aircraft industry as one of the primary targets. Second, the commander of
41 Biddle [2002]; Crane [2016] pp. 14–30; Morris [2017] pp. 112–197.
42 Henke [1993] p. 17.
43 Arai [2008] pp. 73–79.
44 Nakazawa [2014] pp. 81–96; Bennett [2019] p. 22.
45 In addition, economic constraints within the Army Air Corps made precision bombing doctrine desirable.

Biddle [2002] p. 183; Crane [2016] pp. 21–22.
46 Schaffer [1985] p. 35; Webster and Frankland [2006: 1961] pp. 381–417.
47 A military historian Ronald Schaffer detailed that the USAAF’s bombing policy had changed from precision
to area bombing in the European theater. He pointed out that moral consideration had little impact on the process.
Although the USAAF conducted de-facto area bombing, it did not carry out nighttime bombing in Europe.
Schaffer [1985].

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SATOSHI FUJITA
the 21st BC was Haywood Hansell, who had been one of the Bomber Mafia and was anadherent of the doctrine. Third, B-29s were not deployed in the field enough to carry out
area bombings successfully against a city on a broad scale48. In any case, as mentioned
above, Hansell could not garner an achievement with precision bombing and so was
replaced by LeMay as the commander. While he engaged in an area bombing campaign
with incendiaries, LeMay continued precision bombing missions to bring successful results
gradually. Even he, however, could not succeed with nighttime precision bombings49.
By placing in this context nighttime precision bombing with a radar by the 315th BW, its
historical significance becomes clear. That is, it can be said that a series of missions by the
BW is the best example that the latest technologies overcame various difficulties involved
in daytime visual (precision) bombing. These missions had a minor impact on the result of
the war because they were carried out in the final stage of the conflict, and they were aimed
at oil-related facilities, which had not been considered essential targets, as will be detailed
later50. However, this example demonstrates that science and technology are crucial factors
in modern war in that they can make possible operations previously viewed as impossible.
If the war had not ended in August 1945, the USAAF might have returned to its doctrine
and produced results with minimum civilian losses. In other words, if nighttime precisionbombing had been feasible earlier, the USAAF would not have changed its policy to area
bombing with incendiaries. In this sense, this case shows that science and technology havea considerable impact on methods of conducting a war. It will be discussed how the successof the missions by the 315th BW influenced the US’s later methods of engaging in war51.
3-2. What made nighttime precision bombing possible
In the previous section, the author notes that science and technology had overcome the
obstacles involved in daytime visual bombing, a process that can be summarized asfollows: the Radiation Laboratory established at the Massachusetts Institute of Technology
succeeded in developing the AN/APQ-7 (EAGLE) radar, which had a higher resolution
than the existing radar system, the AN/APQ-13; Western Electric received an order for themass production of the EAGLE; it was decided that the B-29B, a variant of the B-29 fornighttime operations, would be equipped with the EAGLE; Bell Aircraft was asked to
produce all B-29Bs, and 653 B-29s were manufactured by September 1945, 311 of whichwere B-29Bs 52. This meant that nighttime precision bombing could be achieved bymobilizing not only science and technology but also the industrial capabilities that couldmass-produce these radars and the bombers equipped with them. Although it is importantthat scientific, technological, and industrial bases could influence the way a war is fought,
this aspect will be examined in other articles. Here, this paper summarizes the facts
48 Fujita [2021].
49 Craven and Cate [1983b] pp. 546–576, 646–653; United States Air Force [1953] pp. 169–172. A historian

John W. Dower said that the news of repeated bombings against cities and massive destruction and Japanese
victims numbed the sensibilities of public and media. For example, on May 30, 1945, the New York Times
reported the 6 bombings on Tokyo caused the deaths of a million, or perhaps 2 million of Japanese. Dower points
out that despite the highly exaggerated numbers, neither the quality paper which reported it nor the American
public who read it had any doubts. Dower [2010] pp. 183–184.
50 A USSBS’s report concluded that “[t]he contribution of the bombing offensive against oil to the Japanese
defeat was therefore negligible. The war had already been won by the blockade.” USSBS, Oil in Japan’s War. p.
65.
51 In the Korean War, the U.S. Air Force tried nighttime operations, including precision bombing with shortrange navigation (SHORAN) radar. USAF [1953] pp. 197–211.
52 The number of B-29Bs produced by Bell was determined from the following websites, Aircraft Serial
Number Search (http://users.rcn.com/jeremy.k/serialSearch.html) and USASC-USAAS-USAAC-USAAF-USAF
Military Aircraft Serial Numbers--1908 to Present (https://www.joebaugher.com/usaf_serials/usafserials.html).

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In Consideration of Nighttime Precision Bombing by the U.S. during World War II
concerning the development of the radar and the production of B-29Bs.
To begin with the development of EAGLE, recommended by Vannevar Bush, who wasthen-president of the Carnegie Institution in Washington, D.C., President Roosevelt
established the National Defense Research Committee (NDRC) in June 1940 and the Officeof Scientific Research and Development (OSRD) in June 1941 to mobilize scientists andengineers in preparation for war. The role of both institutions was not research anddevelopment, instead enabling studies by personnel and research institutions for certain
research and issuing contracts for such53. The OSRD’s funding amounted to half a billion
dollars by the end of the war54. It was the NDRC that recommended the establishment of alaboratory to research primarily microwaves, that is, radar, at the Massachusetts Institute ofTechnology (MIT), eventually becoming the Radiation Laboratory (Rad Lab). In sum, theOSRD funded 114 million dollars to MIT, which was made the biggest contractor of theOSRD55.
EAGLE was developed at Rad Lab, after which flight experiments were successfullycompleted in May 1944. Western Electric initially received an order for 612 EAGLEs, but
it eventually took on the responsibility to produce 1,660. This, however, did not proceedsmoothly. The idea of a higher-resolution radar with high-frequency microwaves had been
embraced as early as November 1941, meaning it took about 2 and a half years to complete
the flight experiments. One reason for such a long time needed was that because thefeasibility of the EAGLE was considered questionable within Rad Lab, it was notnecessarily highly prioritized. Although MIT and Rad Lab were abundant funding,economic and human resources were naturally so limited that Rad Lab had to set priorities
based on the importance and feasibility of each development. The relatively low priority of
EAGLE inevitably led to the delay of the research and development of the equipment andthe achievement of more precise bombing operations56. To make clearer the picture ofnighttime precision radar bombing, it is necessary to place in this context the overall policy
and direction of Rad Lab or the OSRD, but this point will be examined in other articles.
Concerning the production of B-29B, as previously noted, it was B-29B, a variant of the
B-29, that was equipped with an EAGLE, and Bell undertook the production of them all.
Originally, it was Boeing that developed and manufactured B-29s, so why did Bell sign acontract to produce them? As it happened, not only B-29s, but also many goods saw theirproduction charged to companies under license contracts other than those that developed
them. In the case of B-29s, Boeing produced them at the Wichita second plant in Kansas
and the Renton factory in Washington. In addition, government-owned factories wereconstructed at Omaha, Nebraska, and Marietta, Georgia, where Glen L. Martin Company
would operate the former and Bell the latter. It was called government-owned, contractoroperated (GOCO) when private companies operated plants funded federally57. Thus, theproduction of B-29s and B-29Bs had to be placed in the context of U.S. industrial
mobilization.
Since the author has few primary documents to clarify why Bell was charged to produce
53 Stewart [1948] pp. 7–51.
54 Larry Owens notes that the OSRD issued almost 2,300 contracts with 321 industrial institutions and 142

academic and other non-profit institutions. Owens [1994] pp. 526, 565–576.
55 Owens [1994] p. 565.
56 Brown [1999] 192–193; Office of Scientific Research and Development, National Defense ResearchCommittee, Division 14, Radar: Summary Report and Harp Project, vol. 1 of Summary Technical Report ofDivision 14, NDRC, pp. 75–77 (Downloaded from the Library of Congress, https://www.loc.gov/
item/2015490937/ [Last access, March 15, 2024]).
57 For GOCO, see Wilson [2016] pp. 62–83.

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SATOSHI FUJITA
B-29Bs, this paper describes how Bell came to produce B-29Bs and the pace at which they
were manufactured. In January 1940, the U.S. Army Air Corps envisaged a Very Heavy
Bomber (VHB) having a higher performance than the existing Heavy Bombers, such as the
B-17 (Boeing) and B-24 (Consolidated Aircraft Corporation). The USAAF signed acontract with Boeing for prototype aircrafts in September, but concerned with the speed ofcompletion, the USAAF reached agreement with the company for the construction of the
Wichita second plant in June 1941 before prototype flying, and in July, it ordered 1,050
B-29s. Martin and Bell was also asked to build the B-29s 58. In December 1941, theconstruction of a new factory at Marietta was planned, and then in May 1942, it was
decided formally that Bell would operate the plant. Due to the delay in the completion of
the new plant and the lack of manpower, it was as late as November 1943 when Bellproduced their first B-2959; eventually, the Marietta plant would deliver 205 B-29s by theend of 1944, all of which were ordinary B-29s.
As late as around October 1944, the USAAF considered the production of B-29Bs and
B-29Bs equipped with EAGLE60, and in November, it was decided to organize a unit of
EAGLE-equipped B-29Bs. Then, in December, the 315th BW was notified that the special
unit would be their own61, and the first B-29Bs by Bell–Marietta were delivered to the315th BW in February or March 194562. Further, the 16th BG, one unit of the 315th BW,
received an almost authorized force (45 B-29s) by May, and on June 26, the 315th BW
began its first mission. Therefore, it was impossible for the 315th BW, dedicated tonighttime radar precision bombing, to be ready begin start their operations without theeffort of Bell in mass-producing B-29Bs, totaling over 300. However, questions remain:
why was Bell asked to manufacture B-29Bs, what challenges did Bell face with the change
in specifications, and what was the position on B-29B production in the overall B-29
production plan? These are future issues.
3-3. Why were oil-related facilities targeted?
That nighttime radar precision bombing became possible with technological and industrial
bases is a completely different issue from the fact that oil-related facilities were targeted
for operations. In this section, the author explains the reasons for the latter.
The Army Air Corps had adopted precision bombing as its strategic bombing doctrine,
based on which the USAAF identified power plants and oil facilities as important targets inthe European theater. However, the USAAF did not consider oil plants essential to thebombing campaign in the war against Japan. Thus, in November 1943, a report of theCommittee of Operation Analysts (COA)63 listed merchant shipping, steel production, theantifriction bearings industry, urban industrial areas, aircraft plants, and the electronics
industry as strategic targets to be prioritized. The following October, another report of thecommittee set the aircraft industry, urban industrial areas, and shipping (“by all available
means, including mining”) in order of priority64, but neither mentioned oil-related facilities.
58 Craven and Cate [1983b] pp. 6–7.
59 Muelen [1995] p. 54.
60 Lauris Norstad to Curtis LeMay, October 5, 1944, 20th Air Force-Official File (2), Pentagon Series, Project

Subseries, Box 27, Lauris Norstad Papers, 1930–1987, National Diet Library, Japan.
61 Swann [1986] p. 27.
62 Swann [1986] p. 40; Mann [2004] p. 30.
63 COA was created by the directive of Henry Arnold in late 1942 to discuss and recommend bombing target
and analyze “the rate of progressive deterioration that should be anticipated in the German war effort as a resultof the increasing air operations.” Craven and Cate [1983a:1949] pp. 349, 353–354.
64 Craven and Cate [1983b] p. 552.

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In Consideration of Nighttime Precision Bombing by the U.S. during World War II
This is because a blockade or attack on oil tankers directly was more efficient thanbombing inland oil plants, at least concerning the Japanese oil industry. In fact, Japaneseoil production capacity was already reduced by these operations by the time the 21st BC
undertook its operations. Nevertheless, oil-related plants were attacked from June 1945, but
why? To answer this question, AAF in WWII explains:
By April, however, AAF intelligence had come to the opinion that the petroleum
industry in Japan was in so critical a state that the destruction of facilities and stores
would react immediately upon the tactical situation. Consequently, LeMay and Lt. Gen.
Barney M. Giles, who came to Guam as the deputy commander of the Twentieth Air
Force, eventually decided that during its combat-testing period the 315th Wing would
devote its efforts exclusively to oil targets. This decision had the enthusiastic
indorsement of Gen. Carl Spaatz, slated to command all B-29’s under USASTAF [U.S.
Army Strategic Air Force], who had been an ardent advocate of the oil campaign in the
ETO [European Theater of Operations] 65.
The argument that the destruction of oil plants had become “critical” is unsound because
they were bombed sporadically by then, and the Japanese oil production capacity further
worsened due to other operations, such as blockades and mining around the Japanesewaters 66. Two reasons can be offered for why oil facilities emerged as the target ofnighttime precision bombing with EAGLE.
First, there remained few targets that the 21st BC could attack, as the top-priority target,
the aircraft industry, was near utter destruction due to the ongoing efforts of precisionbombing under LeMay’s command. For example, because of missions toward the
Mitsubishi Heavy Industry Nagoya Engine factory and Musashi plant of Nakajima on April
7, as well as Musashi again on April 12, the Musashi plant’s operations came to a halt 67.
Then, on July 24, the final precision bombing of aircraft factories was carried out when 625
B-29s destroyed seven targets. LeMay had modified his tactics, such as using 2,000-poundbombs and lowering the bombing altitude to ensure a precise result. Thus, missions against
the aircraft industry by the newly arrived 315th BW would have a negligible effect.
Besides, by June 1945, the targets of nighttime area bombing shifted from larger cities to
middle and smaller cities, and it was decided at the end of 1944 that B-29Bs equipped with
the EAGLE would be deployed to the 315th BW. In contrast to precision bombing, area
bombing did not necessitate precision attack, and this is because area bombing could be
carried out in nighttime with an existing radar. Therefore, it must be nonsense that an
EAGLE-equipped unit would carry out such missions. Over 60 Japanese cities were leveledby area bombing campaigns, despite a study of new targets in June 1945 listed only 25
cities. In retrospect, the destruction of over 60 cities can be judged excessive. The
incremental build-up of the 21st BC led to the excessiveness. Sorties of the 21st BC permonth had risen steadily, along with the number of B-29s deployed to Marianas (Figure 1).
If the 315th BW had joined the campaign against middle or smaller cities, only some lesssignificant cities would have been added to the list of cities destroyed. In sum, it would
have been unnecessary for the 315th BW to attack existing targets with other units.

65 Craven and Cate [1983b] p. 660.
66 USSBS, Oil in Japan’s War, pp. 45-66.
67 Craven and Cate [1983b] pp. 647–648.

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SATOSHI FUJITA
Figure 1. Sorties per Month and B-29s Deployed to 20th AF

Source: Koyama [2018] and the Office of Statistical Control [1945].

Therefore, another target system for the 315th BW was needed, but oil plants showed
little reason to be attacked. Nevertheless, they were chosen as targets for the unit because
they were considered best for the “test” of the newly developed radar set, which is thesecond reason oil plants were selected. Furthering this point, an official history of the 315th
notes, “Japan’s oil refineries provided ideal test targets because they were relatively
undamaged, well-defined, and located near the coastline,” so bombardiers could easily
identify their targets with EAGLE 68. Werrell suggests that if the war had not ended inAugust, the 315th BW, which completed the test successfully, would have conductedmissions to more significant inland targets, including bridges69. Indeed, the USAAF set
railroads and stations as primary targets in the final days of the war, and on August 14, thelast day of the war, the 21st BC bombed the Marifu railroad yards (Iwakuni station) in
Yamaguchi with 115 B-29s, a mission that implies a gradual shift in priority from urban
areas to transportation systems.
There were other cases in which modern technologies or embraced tactics were “tested”
in battlefields. For example, the firebombing against Tokyo on February 25, 1945, wascarried out as test of area bombing with incendiaries, and the success of this test led to the
March 9–10 air raid. (Other tests were conducted on Nagoya on January 3 and Kobe on
February 4, but they were judged as failures.) More explicit instances include the atomic
bombings. Where and how the atomic bombs would be used was discussed from April
1945. Further, it was decided in an earlier phase that the bombs would be used against
cities of a certain size. When desirable cities were selected, the condition was that any
68 Swann [1986] p. 123; Werrell [1996] p. 199.
69 Werrell [1996] p. 199; Swann [1986] p. 122.

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In Consideration of Nighttime Precision Bombing by the U.S. during World War II
target city should face minor damage from strategic bombing by the time of the atomic
bombings, so the suffering from the nuclear attacks could be examined. Because this would
be impossible if target cities were leveled, strategic bombing missions were prohibitedagainst cities listed for the A-bomb, including Kyoto, Hiroshima, and Kokura. These facts
suggest that Hiroshima and Nagasaki were not the most important strategic targets for
destruction as early as possible, which was the case with petroleum facilities.

Conclusion
This article summarizes the nighttime precision bombing campaign using the new radar by
the 315th BW, which demonstrates its historical significance and suggests the challenges topainting a clearer overall picture. Although this campaign had a negligible impact on theconsequences of World War II, it is of great historical significance in that the industrial,
scientific, and technological mobilization enabled the realization of missions previously
considered impossible. The way of engaging in war itself depended on the wartime
mobilization of industry, science, and technology, and importantly, the timing of themissions and their feasibility depended on the priorities in research and development andthe pace of weapons and equipment production. If the USAAF had achieved precisionbombing earlier, would it have carried out an area bombing campaign on such a scale?
To clarify the overall picture of the nighttime precision bombing campaign with radar, thefollowing problems must be addressed. The first is how industrial, scientific, andtechnological bases were established to make possible such a campaign. Rad Lab at MIT
developed EAGLE, so the history of its development should be clarified by placing it in thecontext in which the Rad Lab was set up and the overall research trends at the time. In
addition, Bell assumed the production of B-29Bs equipped with EAGLE, so it must be
explained how and why the AAF contracted with Bell. In doing so, the contract should beplaced in the overall picture of the development and production of B-29s. Second, it must
be understood in detail why petroleum facilities were chosen as the targets of EAGLE
missions. As already mentioned, the choice of oil facilities strongly implies that themissions had an experimental aspect, which seems to reflect how the U.S. military engagedin war. Therefore, it can be said that a clearer understanding of the precision bombing
campaign with EAGLE would shed light on how the war was fought by the U.S. military.

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[This work was supported by JSPS Kaken Grant Number 21K13131. I appreciate anonymous reviewers fortheir valuable comments.]

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