War Game: B-17 vs. Destroyer

General PurposeAnalytical
Scope and LevelRange of Command Levels
Tactical

Military Services Involved

U.S. Army Air Force, Imperial Japanese Navy

Type of Operations

Air-to-Surface Engagement

Area of Operations

Off the western coast of the Philippine island of Luzon

Number of Sides2
Amount of IntelligenceOpen
Method of EvaluationRigid
Basic Simulation TechniqueComputer

As with our tanks versus battleship war game, this is less of a pure analytical game and more of a test of the simulation’s capabilities.

Historical Background

In a previous post on IJN Aerial Attack Tactics, it was noted that in WWII it was mathematically possible for horizontal bombers to hit a moving target, but that the probability of a successful hit approached zero if the target was successful at maneuvering out of the dispersion area of the bombs. It was also noted that both the Imperial Japanese Navy and U.S. Navy studied the efficacy of high-level bombing on naval targets prior to the war. Bombing tests during the interwar years had the U.S Navy originally assess horizontal bombing accuracy from a release altitude of 12,000 feet to be 20% in 1934, however, by 1938, this was reduced to 8% (Nofi, 2010, p. 306-307). Actual wartime combat experience showed that high-altitude horizontal bombing from an altitude of between 8,000 – 12,000 feet against maneuvering targets had an accuracy that approached zero, even under the most favorable conditions (Nofi, 2010, p. 34). The only warship to be arguably “sunk” by such a method was the destroyer Mutsuki on August 25, 1942, at 1027 in the “Slot” northwest of Guadalcanal (Nofi, 2010, p. 34-35). As the Mutsuki slowly maneuvered (i.e. taking no evasive action) to rescue survivors from the disabled troop transport Kinryu Maru, three B-17s spotted them and attacked. However, the captain, Commander Hatano, knowing the poor accuracy of high-level bombers paid no mind to them and did not make any attempts to evade. For his foolishness, the Mutsuki was hit by one bomb which detonated in the engine room. The Mutsuki sunk around 1140 with the loss of forty men. Commander Hatano later said during his interrogation that “Even the B-17s could make a hit once in a while” (Frank, 1992, p. 191). Unfortunately, I’ve been unable to find any source that notes how many bombs were dropped or at what altitude the three B-17s bombed the Mutsuki. There’s at least one other instance of B-17s successfully hitting a destroyer. On the morning of August 19, 1942, the Japanese destroyer Hagikaze suffered three direct hits on her stern that killed 33 and wounded 13 (Frank, 1990, p. 147). Allyn Nevitt (1998) notes that Hagikaze was only hit by one bomb, but it destroyed her #3 turret, flooded the magazine, damaged her rudder and propeller shafts, and reduced her speed to 6 knots (para. 18). Regardless of the number of hits she took, she didn’t sink and was escorted out of the area by the destroyer Arashi. It should also be noted that there are several other instances of Japanese successfully hitting U.S. ships with level-bombing, but those instances didn’t result in sinkings and didn’t involve B-17s, so we’re disregarding them for this test.

Situation

During WWII many different types of warships from destroyers to capital ships were hit and/or sunk by dive-bombing, skip bombing, torpedo bombing, suicide bombing, and even early guided weapons like the Fritz X bomb. However, for the sake of keeping this war game and the subsequent analysis focused, we’re only looking at the B-17’s level bombing accuracy against a destroyer-sized target. An examination of the efficacy of different methods of bombing against different types of ships is for further wargames. Therefore, given what we know about the historical inaccuracy of high-level bombing and the fate of the Japanese destroyer Mutsuki, can we conduct tests in Command: Modern Operations using level-bombing with B-17s and come to similar results?

In other words, our essential question to answer is:

Does the accuracy of B-17s conducting level bombing at various altitudes against a destroyer-sized target, coincide with either the historical accuracy of nearly zero when dropped between 8,000 – 12,000 feet, or the 1938 assessed accuracy of 8% at 12,000 feet?

An additional essential question to answer is:

(With the same engagement parameters) For the bombs that do hit the target, how many hits are required to successfully sink a destroyer-sized target?

For this scenario, there were three B-17G Flying Fortress bombers, each armed with 12x M64 500-pound bombs, attacking one Fubuki-class destroyer (CMO‘s databases don’t contain a Mutsuki-class DD, so I substituted a Fubuki). I conducted ten tests at each preset altitude. Drop altitudes were at 36,000 feet; 25,000 feet; 12,000 feet; 2,000 feet; 1,000 feet; and 800 feet. The last set of tests were at a drop altitude of 800 feet because that is the minimum drop altitude for the M64 bomb, as oppose to the minimum altitude (80 feet) that the pilots (with “normal” proficiency) can fly the aircraft. For the sake of efficiency, it was assumed that the B-17s had already located the destroyer and determined that it was hostile.

Video

Forces

B-17G Flying Fortress (USAAF) [Player]Fubuki DD (1943 refit) (IJN) [A.I.]
3 aircraft1 vessel
Type: Bomber
Crew: 13
Span: 33 m
Height: 6 m
Length: 22.2 m
Max Payload: 2723 kg
Empty Weight: 16391 kg
Max Weight: 24500 kg
Operator: United States Army Air Force
Commissioned: 1943
Propulsion: 4x Wright R-1820-97

Damage Points: 10

Type: DD – Destroyer
Crew: 219
Max Speed: 38 kt
Beam: 10.4 m
Draft: 3.2 m
Length: 118.5 m
Displacement: 2050 t
Operator: Imperial Japanese Navy
Commissioned: 1943
Propulsion: 2x Kampon Geared Turbines

Damage Points: 350
Sensors:
Director/VB-GBVisual, Bomb Sight
Max Range: 3.7 km
Optical/Norden Bombsight
Visual, Bomb Sight
Max Range: 3.7 km
Optical/GB-4 CCTV Unit
Visual, Bomb Sight
Max Range: 3.7 km
Sensors:
Type 2 Mark 2 Model 2 – Radar, Surface Search & Navigation
Max Range: 64.8 km
Type 3
– Hull Sonar, Active-Only Search & Track
Max Range: 1.9 km
Type 91 director
– Radar, FCR, Weapon Director
Max Range: 29.6 km
Type 95 director
– Visual, Optical Sight
Max Range: 27.8 km
HF/DF
– ESM HF/DF
Max Range: 1481.6 km
*Characteristics from the game database. Data may vary from official sources.

Comparison of Weapons

M64 500lb GPB – Bomb
Surface Max: 1.9 km. Land Max: 1.9 km.
Warhead: 192 pounds of Tritonal (130.5 damage points).
Circular Error Probable (CEP): 200m (656ft).
12 bombs/aircraft.
127mm/50 3rd Year Twin AA-VT Burst [2 rnds] – (Anti-Aircraft Frag) Gun
Air Max: 2.8 km. Surface Max: 16.7 km. Land Max: 16.7 km.
127mm/50 3rd Year Twin HiCap Burst [2 rnds] – Gun
Air Max: 2.8 km. Surface Max: 16.7 km. Land Max: 16.7 km.
25mm/60 2M-3 Twin Burst [20 rnds] – Gun
Air Max: 1.5 km. Surface Max: 2.8 km. Land Max: 2.8 km.
25mm Type 96 [20 rnds] – Gun
Air Max: 1.5 km. Surface Max: 2.8 km. Land Max: 2.8 km.
*Depth charges and torpedoes have been omitted since they have no bearing on anti-air threats.
*Characteristics from the game database. Data may vary from official sources.

The General Purpose Bomb (GPB), such as the M64 500-pound bomb, primarily achieved their effects through high explosive blast fragmentation. They could be equipped with both a nose and a tail fuse for either instantaneous or slight delay detonation (Depts. of Army, Navy, & Air Force, 1966, p. 2-18). However, CMO doesn’t specify which fuses are used.

Note that the the Fubuki‘s weapons have a fairly low ceiling of engagement for air targets. The 127mm/50 gun has a maximum range for air targets of 2.8 kilometers or ~9,186 feet and the 25mm can engage air targets at 1.5 kilometers or ~4,921 feet. Therefore, we can expect the bombers to be engaged by AA fire (and perhaps sustain damage or losses) anywhere below roughly 10,000 feet. Some models of the 127mm/50 gun could be elevated to 75 degrees, but the ammunition had to be hand loaded at 5-10 degrees of elevation. Realistically, the 127mm gun was useless as an AA weapon owing to the slow rate of train and elevation (Campbell, 1985, p. 192). The 25mm gun was not particularly effective, either. Japanese crews reported that the twin and triple mounts, either powered or hand-worked, elevated and trained too slowly. Furthermore, the sights were poor for fast moving targets, the magazines were too small, and there was excessive muzzle blast and vibration in the mounts (Campbell, 1985, p. 200). Postwar interrogations further indicate that the 25mm gun was ineffective beyond ranges of 2,000 meters or heights of 1,000 meters. Attempts to engage targets beyond those ranges essentially wasted ammo (U.S. Naval Report O-44, 1946, p. 7). Of course, this does not mean that the weapons were incapable of performing in the AA role, merely that they were very poor at it. All that being said, this war game is not examining the effectiveness of Japanese AA weapons, so we’re not gathering data on how often the B-17s get shot down.

Things that impact bombing accuracy:

  • Unit Proficiency: Regular (higher proficiencies are more accurate with unguided weapons)
  • Type of Bomb sight: Norden ballistic sight (ballistic computer) imparts a 25% reduction on bomb CEP
  • Type of Bomb: M64 500-pound bomb. Unguided bomb.
  • Weather: Clear skies, no rain, 25C, wind/sea state 1. (i.e. Ideal conditions for bombing.)

What is Circular Error Probable (CEP)?

Circular Error Probable (CEP) is a measure of a weapon’s precision within a circle of a given radius. Essentially, it states that when aimed at the same target, 50% of the weapons will fall within the given radius of a target. For example, if a weapon has a CEP of 100 meters, and 100 rounds are fired at the same point, then 50 of those rounds will fall within 100 meters of that point/target.

In the case of our 500-pound bombs, note that they have a CEP of 200 meters (656 feet). Also, recall that the Norden bomb sight (ballistic computer) imparts a 25% reduction on an unguided weapon’s CEP. Therefore, the revised CEP for the M64 500-pound bomb would be 150 meters (492 feet).

Bomb Warhead

Command‘s database notes that the M64 bomb warhead is a Mk82 bomb filled with 192 pounds of Tritonal. Obviously, these are technically two different weapons, albeit both general purpose bombs. See below:

This may seem strange because the Mark 80 series of bombs did not enter service until post-WWII, however, recall that Command‘s Cold War Database is technically post-WWII to 1970, but it contains weapons, sensors, and platforms from WWII that were still in use after the conflict ended. So for all intents and purposes, they’re the same thing. Historically, the M64A1 500-pound bomb had an explosive warhead of either TNT (266 pounds), Composition B (273 pounds), Tritonal (283 pounds), or Amatol (262 pounds). The warhead comprised approximately 50% of the bomb’s overall weight. In reality, the actual weight of the bomb would be heavier with tail fins, and a TNT-filled 500-pound bomb would weigh 548.69 pounds (Depts. of Army, Navy, & Air Force, 1966, p. 2-23 – 2-24).

While CMO‘s use of a Mk82 192 pound Tritonal warhead doesn’t match the 283 pounds of Tritonal in the historical M64A1, it should be noted that the game uses an equivalent amount of TNT to measure a warhead’s explosive damage. According to the game FAQ on WarfareSims.com, 1 Damage Point (DP) = 1 kilogram of TNT, and the game automatically converts various explosives to TNT equivalents with 1 kilogram of Tritonal = 1.5 kilograms of TNT. With that conversion in mind, in the case of the M64 500-pound bomb, 192 pounds (87.1 kilograms) of Tritonal = 288 pounds (130.65 kilograms) of TNT. Therefore, it should do 130.65 DPs (according to the game’s TNT equivalency). The 288 pounds of equivalent TNT would equate to ~57% of the weight of a (purely) 500-pound bomb, or ~52% of the weight of a 548.69 pound bomb with tail fins. So, while the amount of Tritonal is not historically accurate for the M64A1, the TNT conversion is 22 pounds more than the historical amount of TNT and roughly accurate to the warhead’s proportional weight.

The Fubuki possesses 350 Damage Points (DP) worth of health. We know that the M64 bombs cause 130.65 DP, so mathematically speaking it would take ~2.68 M64 bombs to destroy the Fubuki. According to Youtuber P Gatcomb (2020), high explosive (HE) weapons have an 80% reduction in effectiveness against armored targets. Although in his video, he calculates HE as having 80% effectiveness against armor (i.e. a 20% reduction in effectiveness), rather than an 80% reduction in effectiveness. However, destroyers have no armor, so the HE bombs should not suffer any reduction to their effectiveness.

Analysis of Results

Note 1: The data I collected originally included the distances missed by the bombs. However, since I haven’t found any historical data on how precise the bombs were, there’s nothing to establish precedence against, and therefore no point in measuring precision (i.e. how far they missed their target). To that end, in this wargame, we’re only concerned about accuracy (i.e. whether the bombs hit the destroyer or didn’t).

Note 2: Unfortunately, the game doesn’t specify what a “malfunction” is. It could be that the bomb failed to release when dropped or failed to explode upon impact. No further information is given in the message log apart from the fact that the “weapon malfunctioned.” Therefore, unless specifically noted, malfunctions have been omitted from data entries.

Table #1: Number of Hits & Sinkings

Drop Altitude >>36,000ft.25,000ft.12,000ft.2,000ft.1,000ft.800ft.
Test 101 (93%)0000
Test 2001 (97%) “S”000
Test 301 (86%)000 “S”0
Test 400003 (96%, 100%, 97%) “S”1 (100%) “S
Test 5001 (100%) “S”000
Test 6000000
Test 702 (88%, 100%) “S”0001 (100%) “S”
Test 801 (91%) “S”3 (100%, 100%, 100%) “S”02 (100%, 100%) “S”0
Test 90004 (96%, 100%, 100%, 96%) “S”2 (100%, 87%) “S”0
Test 10002 (86%, 85%) “S”01 (100%) “S”0
Totals0Hits: 5
Sunk: 2x

Avg. Penetration: 91.6%
Hits: 7
Sunk: 4x

Avg. Penetration: 95.43%
Hits: 4
Sunk: 1x

Avg. Penetration: 98%
Hits: 8
Sunk: 5x

Avg. Penetration: 97.5%
Hits: 2
Sunk: 2x

Avg. Penetration: 100%
Data indicates the number of direct bomb hits on vessel for given altitude and test number. Percentages indicate the amount of penetration of the hit(s). “S” indicates vessel was sunk.

All of the bombs that hit the target achieved 86% penetration or greater. Since these were unarmored targets, it’s unknown how much of a factor this penetration was in the amount of damage caused. While the log notes damage such as fires and flooding, it’s unknown if this was caused by the bomb penetrating the deck. (Presumably it was, but we shouldn’t make assumptions about how “tactically detailed” the game is. Remember that it’s primarily an operations simulator.) Note that Test 3 @ 1,000 ft. indicates zero hits and a sinking, but the vessel was sunk due to near miss damage.

The highest number of hits attained in a single test was during Test 9 at 2,000 feet which saw 4 bombs hit the Fubuki. However, that was also the only test out of ten at that drop altitude that achieved any hits. Overall, the highest number of total hits achieved in ten tests was at a drop altitude of 1,000 feet which recorded hits in 4 of the tests for a total of 8 hits. The second highest number of hits achieved in ten tests was at a drop altitude of 12,000 feet which recorded a total of 7 hits in 4 of the ten tests. Similarly, the tests conducted at drop altitudes of 12,000 and 1,000 feet also recorded the highest number of times that the Fubuki was sunk (4 and 5 times, respectively).

Table #2: Totals

Drop AltitudeBombs DroppedHitsMalfunctions
36,000ft.3600 (0%)7 (1.90%)
25,000ft.3605 (1.39%)8 (2.22%)
12,000ft.3607 (1.94%)6 (1.67%)
2,000ft.3604 (1.11%)5 (1.38%)
1,000ft.3248 (2.50%)8 (2.50%)
800ft.3472 (0.58%)7 (2.02%)
Totals represent aggregate data from ten tests conducted at each drop altitude. Malfunctions have been included in the total number of bombs dropped.

Figure #1: Bar Graph of Totals (minus # of bombs dropped)

The data from Table #2 and Figure #1 displays the total number of bombs dropped, hits, and malfunctions for all tests at the given altitudes. The variation in the total number of bombs dropped during the tests at 1,000 feet and 800 feet was a result of the target being sunk before all three bombers could drop their bomb loads (e.g. two of the bombers dropped their bombs and sank the target, therefore negating the need for the third bomber to drop its bombs). As for the number of hits achieved, the numbers vary, but the highest number of hits was 8 in total at a drop altitude of 1,000 feet. Only at a drop altitude of 36,000 feet were no hits made in a total of ten tests conducted. The number of malfunctions within ten tests varied between 5 and 8 out of the more than 300 bombs dropped in total at each altitude.

Evaluation

Remember that this wargame is specifically looking at the effectiveness of level-bombing against a destroyer-sized target and not any other method of bombing against any other type of vessel.

Hits and Sinkings

From the data gathered on hits and sinkings, we can answer our first and second essential questions:

Does the accuracy of B-17s conducting level-bombing at various altitudes against a destroyer-sized target, coincide with either the historical accuracy of nearly zero when dropped between 8,000 – 12,000 feet, or the 1938 assessed accuracy of 8% at 12,000 feet?

Answer:

According to the collected data in Table #2 and Figure #1, when dropped at 12,000 feet, the total number of bombs (360) dropped in the 10 tests resulted in a total of 7 hits, or 1.94%. This is below the 8% accuracy assessed in the 1938 tests, but above the nearly zero percent in terms of historical data. Thus, the simulation value falls in-between the two and doesn’t coincide precisely with either of the historic values. That being said, even the best hit percentage was roughly 2% which is abysmal, so I wouldn’t write the simulation off as inaccurate. More tests are likely needed, especially with drop altitudes specifically at 8,000 feet. Additionally, we don’t know the precise parameters of the historical data, so any test we do in CMO is merely an approximation of both the real world data and of the simulation’s capabilities. We can probably write the number of hits off as products of mere chance since the game does a dice roll to determine combat outcomes.

However, overall, there appears to be no discernible trend indicating an increase in the number of hits achieved as the release altitude decreased apart from the fact that no hits were achieved in the ten tests conducted at 36,000 feet. That being said, the tests conducted at 12,000 and 1,000 feet appeared to be the most successful with the most recorded hits and sinkings.

Another thing of note is that a review of the footage shows the three bombers largely attacking along the Fubuki‘s longitudinal axis. This is to say that the Fubuki was always headed south towards its patrol area while the bombers attacked from that direction. In other words, the destroyer was heading south while the bombers were heading north, and the ship got in the way of the bombs on a few occasions. Perhaps if the bombing was conducted perpendicular to the longitudinal axis of the ship, then we would see different results. Perhaps we would see less hits (and consequently less sinkings) in that case.

(With the same engagement parameters) For the bombs that do hit the target, how many hits are required to successfully sink a destroyer-sized target?

Answer:

The data in Table #1 would suggest that at least one direct bomb hit was required to sink a destroyer-sized target, although that was not guaranteed to sink the vessel, as is indicated in Tests 1 & 3 from a bombing altitude of 25,000 feet. Despite their significant penetration, those were the only two instances of single bomb hits not sinking the target. All other instances of single bomb hits resulted in the target being sunk. This is in contrast to the previous mathematical conclusion that a Fubuki-class destroyer with 350 DP would require ~2.68 M64 500-pound bombs doing 130.65 DP each to destroy it. That being said, all instances where two or more bombs hit were sufficient to sink the destroyer. From this data, we can conclude that a single 500-pound bomb hit was very likely to sink the destroyer (or at least cause severe damage and likely disable it), whereas two or more hits were guaranteed to sink it. Thus, assuming a best case scenario with the highest hit percentage of 1.94% at a drop altitude of 12,000 feet, out of 100 bombs dropped, at least one (perhaps two) were likely to hit and sink the destroyer.

The deciding factor was likely how much damage the bomb did in terms of creating fires and/or flooding. The message logs generated by the game recorded that even a single bomb hit caused significant damage to any topside equipment. Whether or not the bomb penetrates, and the amount of penetration would be somewhat irrelevant since destroyers aren’t armored and the bombs are not armor-piercing or semi-armor piercing. Therefore, we can conclude that if a bomb hits the destroyer, then it is virtually guaranteed to penetrate the deck.

Alternatives

Since this game was more or less a test of the simulation’s capabilities, we’ll ignore any alternatives that suggest different platforms that could have different weapons and/or performance characteristics. That said, here are some possible alternatives to this game:

  • Additional tests at each altitude and at different altitudes may show different results that may or may not align with the assessed historical values.
  • Different bomb load-outs for the B-17s may produce different hit percentages depending on the weapon used.
  • A different number of destroyers and/or attacking B-17s may produce different results.
  • Higher/lower unit proficiencies would increase/decrease the accuracy with unguided weapons. Thus, the bombers may be more accurate with their bombs and the destroyer may be more accurate with its AA fire.
  • Different times of day or weather may produce different results.

References

Campbell, J. (1985). Naval Weapons of World War Two. Naval Institute Press.

Departments of the Army, Navy, and Air Force. (1966). TM 9-1325-200/NAVWEAPS OP 3530/TO 11-1-28 Bombs and Bomb Components. U.S. Government.

Frank, R.B. (1992). Guadalcanal: The Definitive Account of the Landmark Battle. Penguin Books.

Nevitt, A.D. (1998). IJN Hagikaze: Tabular Record of Movement. Nihon Kaigun. http://www.combinedfleet.com/hagika_t.htm.

Nofi, A.A. (2010). To Train the Fleet for War: The U.S. Navy Fleet Problems 1923-1940. Naval War College Press.

P Gatcomb. (2020, January 15). Command: Modern Operations Tutorial – Bombing [Video]. Youtube. https://www.youtube.com/watch?v=bPVkIPVlNlA.

U.S. Naval Technical Mission to Japan. (1946). Report O-44: Effectiveness of Japanese AA Fire. Archive.org. https://web.archive.org/web/20120501094911fw_/http://www.fischer-tropsch.org/primary_documents/gvt_reports/USNAVY/USNTMJ%20Reports/USNTMJ-200F-0370-0383%20Report%20O-44.pdf.

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