WW2 US Submarine Torpedo Firings Versus Time

Quote of the Day

If you can’t describe what you’re doing as a process, you don’t know what you’re doing.

W. Edwards Deming, guru of statistical quality control. I took a class from Dr. Demming in the early ’80s. The older I get, the smarter he seems. He was kind of a cantankerous gentleman (for example, railed constantly against management), but very wise on human behavior in the manufacturing environment.


Figure 1: US Acoustic Homing Torpedo (Torpedo Mk 27).

Figure 1: US Acoustic Homing Torpedo (Torpedo Mk 27).

I recently noticed that combinedfleet.com has excellent summaries of the WW2 US submarine patrol reports that are very easy to scrape for data. These patrol reports are interesting because they provide accurate data as to the rate of torpedo firings by US submarines and some indications as to the mix of torpedoes being fired. Like all WW2 records, not every patrol recorded the weapons used and it is difficult to know how accurate the hit count is.

I will scrape the patrol report pages for 238 submarines and turn the data into graphs and tables that provide insight as to the tempo of US submarine combat in WW2. My workbook is available here for those who like to follow along with the analysis. Note that I used a VBA routine to extract URLs.


WW2 Data Warning

This post is focused on using WW2 historical data to illustrate how to perform data scraping operations. I should note that the results I obtain here vary slightly from results published in other sources, which I show below. This is a common problem with WW2 sources. Often, the results are different because of OCR errors — to be clear, I do not know the source of the difference here.

Definition errors are also an issue – like what constitutes a torpedo (for example, an air-launched homing torpedo deliberately mislabeled as a Mk 21 Mine). Finally, the skippers on some of the patrol reports in some cases simply didn’t say what kind of torpedo they launched. They were busy at the time and can be forgiven for simple omissions.

Alternate Reference

The book Ship Killers (Widenberg and Polmar) has two tables that contain similar information. As is typical for WW2 information, the data between the two tables do not agree in terms of weapons used and totals. However, the results are similar to what I obtained by scraping the Combined Fleet website in broad terms.

Table 1 shows the number of torpedos fired by type and their hit rates. Note that I generally do not give much credence to hit counts because of the difficulty of confirming the information, while the number of torpedoes fired is fairly easy to tally.

Table 1: Torpedoes Fired By U.S. Submarines In World War 11.
Type Fired Hits Percentage
Mk9, 10 11 1,722 502 29%
Mk 14 6,852 2,437 36%
Mk 18 3,536 979 28%
Mk 23 2,058 822 40%
All others 139 39 28%
Total 14,307 4,779 33%

Table 2 shows the number of torpedoes fired by year and theater. Note that the Pacific theater dominated US torpedo usage.

Table 2: US Submarine Torpedo Effectiveness.
Theater Year Fired Hits Effectiveness
Pacific 14,264 4,767 33%
1941 104 13 13%
1942 1,926 554 28%
1943 3,761 1,298 34.5%
1944 6,108 2,329 38%
1945 2,365 573 24%
Atlantic 47 12 25.5%
1942 19 4 21%
1943 24 8 33%
1944 4 0 0%
Total 14,311 4,779 33%

Torpedo Variants

Table 3 shows the torpedoes listed in the patrol reports. Other weapons included in the report are the deck gun, burning, and ramming. I do not address those weapons in this post.

Table 3: Torpedoes Listed in Patrol Reports.
Torpedo Type Description
Acoustic Seeking Torpedo Probably a Mark 27 Cutie
Mark X Torpedo Obsolete, had a depth control issue
Mark X Type 3 Torpedo Obsolete, had a depth control issue
Mark XIV Torpedo Problematic US WW2 standard torpedo
Mark XIV Type 1 Torpedo Problematic US WW2 standard torpedo
Mark XIV Type 3 Torpedo Problematic US WW2 standard torpedo
Mark XIV Type 3A Torpedo Fixed US WW2 standard torpedo
Mark XV Torpedo Surface ship torp, launchable from submarine aft tubes
Mark XVIII Electric Torpedo US copy of German electric torpedo
Mark XVIII Type 1 Torpedo US copy of German electric torpedo
Mark XXIII Torpedo Single-speed Mk 14.



The analysis approach is straightforward:

  • Generate a list of URLs with submarine patrol data
  • Create a Power Query function that grabs the data from each URL.
  • Run the function on each submarine’s URL.
  • Create a consolidated data file.
  • Generate required plots and tables.

Torpedoes Fired Versus Time

Figure 2 shows US torpedo firings by month during WW2. You can see that October 1944 was a very busy month. At the end of the war, the torpedo firings dropped dramatically because most Japanese ships had already been sunk.

Figure 2: US Torpedo Expenditures By Month.

Figure 2: US Torpedo Expenditures By Month.

We can generate a table of yearly data as shown in Table 4. This is very similar to Table 2 from an alternate source.

Table 4: Sub Patrol Torpedo Firings By Year.
Year Torps Fired
1941 104
1942 1,946
1943 3,804
1944 6,165
1945 2,401
Total 14,420

Torpedoes By Type

Table 5 shows the breakdown of the torpedoes fired by type. I assumed that “Acoustic Homing Torpedo” was a Mark 27 “Cutie” for this table.

Table 5: Sub Patrol Report Torpedo Breakdown By Type
Torpedo Claimed Hits Torps Fired Hit Percentage
Mark 14 2,452 6,977 35%
Mark 23 Electric 986 2,595 38%
Not Stated 664 2,321 29%
Mark 18 624 2,149 29%
Mark 10 31 157 20%
Mark 15 46 113 41%
Mark 27 Acoustic Homing 34 108 31%
Grand Total 4,837 14,420 34%


I learned a number of things during this analysis:

  • October 1944 was the peak month of US torpedo firings.
    This seems reasonable. The Japanese still had a significant maritime fleet and the US finally had deployed a significant number of submarines and finally had a working torpedo.
  • Mark 15 torpedoes were used on submarines early in the war.
    The Mark 15 is larger than the Mark 14 and could only be fired from the aft tubes (reference). I knew that torpedoes were in short supply early in the war, so it does not surprise me that they were used if available.
  • There were significant numbers of Mark 18 electric torpedoes fired.
    This is amazing considering the Mark 18 was copied from a German design and was copied, manufactured, and produced in significant numbers during the US’s 44-month wartime involvement.
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2 Responses to WW2 US Submarine Torpedo Firings Versus Time

  1. Ronan Mandra says:


    I was curious about Power Query and how you got your results. So, I did some digging using both Power Query and MS Access. My answers at the basic level are the same as yours with the exception of the Mark 23 and Mark 18 results. According to your notes, the Mk 23 electric is a single-speed Mk 14. According to the Mk 14 wiki, it’s not an electic torpedo. The Mk 18 was an electric torpedo. So, I believe your Mk 23 electric summary consisting of Mk 18 and Mk 23 numbers is in error.

    Also, for the fun of it, I downloaded all columns of the submarine data from the combinedfleet.com website and took a look at the ships sunk or damaged by U.S. torpedoes. The top 5 categories of ships sunk or damaged are: 1500 cargo ships (target code AK), 409 fuel oiler tankers (target code AO), 246 target code SAM ships, 195 transport ships (target code AP), and 169 target code SMC ships. I could not find what the ship codes SAM and SMC represent. I used https://www.history.navy.mil/research/histories/ship-histories/abbreviations.html to determine a number but not all of those target codes in the downloaded data.

    As always, thanks for sharing your thoughts.

  2. Ronan Mandra says:

    Note that my numbers for the top 5 categories of ships sunk exclude those with Lat/Lon errors or date errors.


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