WWII Convoy Tactics

Backstory

During the height of the pandemic, I was under a great deal of stress, so I started listening to a naval history podcast by Drachinifel. The combination of a topic I was already somewhat interested in and the soothing British accent provided me an anchor in the maelstrom of uncertainty I was in. This lead to, after about a year, my large interest in naval history. I spent a good deal of sophomore year exploring naval archives and pouring over deck plans. I took IB History of the Americas Specifically because I knew I would have an opportunity to do a large project on history. Imagine my excitement to find out that my IB History teacher, Ms. Lewell, is a huge naval history nerd. This is the result of that project that I took a whole class just to do!

To what extent did tactical and technological developments change the outcome of convoy battles HX 79 and HX 228?

Introduction

Being an island nation, the United Kingdom (UK) is dependent on overseas imports for essential resources. During the Second World War (WWII), the Kreigsmarine[1] attempted to force the UK to surrender by instituting a blockade. While the blockade did contain some surface elements, the most famous and deadly part of the blockade were U-Boats (Unterseeboot). To reduce the number of sinkings, the Allies gathered ships into convoys and provided them with escorts. Despite this, many ships were sunk, until better Antisubmarine Warfare (ASW) tactics were developed. This investigation aims to analyze the development of those tactics using the Battles of HX.79 in October 1940 and HX.228[2] in March 1943.

[1] German navy

[2] Note: HX indicates an Allied eastbound convoy departing from Halifax

Evaluation of Sources

In investigating these two battles, two sources were particularly useful. Source A, OEG Report No. 51: Antisubmarine Warfare in World War II, a post-war report compiled by the US Navy Department’s Operations Evaluation Group.[1] It contains both a history of submarine and ASW operations during WWII and a detailed discussion of tactics and their development. Source B, Battle of the Atlantic, by Marc Milner, provides a good discussion of both convoy battles and a discussion of ASW tactics from the British Commonwealth perspective.[2]

The OEG report is a good source for basic information regarding the battles, but being a US made report, a greater significance was placed on US action. The only US involvement in the two battles selected was a hunter-killer group consisting of escort carrier ACV/CVE-9 USS Bogue and Clemson-class DD-196 and DD-251 defending HX.228.[3] Nevertheless, it provides good coverage of the tactical side of ASW operations, along with a fantastic view of strategic ASW operations.

Battle of the Atlantic was published in 2003 by Mark Milner, an established naval historian. His PhD thesis, "No higher purpose: the Royal Canadian Navy's mid-Atlantic war 1939–1944" is focused on the convoy war, and he has continued his research on that topic. It is safe to say that he is one of the foremost historians for the Convoy War. Milner discusses tactics in detail, which is absolutely essential to answer the research question. Particularly, his inclusions of diagrams of convoy formations and search patterns is very useful for answering the detailed changes in tactics.

[1] (Sternhell and Thorndike 1946)

[2] (Milner 2003)

[3] (Garner and Hiestand 1998)

Investigation

Attack on HX.79

Convoy HX.79 departed from Halifax, Nova Scotia on 8 October 1940 escorted by an armed merchant cruiser, a destroyer, and 5 smaller escorts. The convoy was commanded by Rear Admiral W. B. Mackenzie from freighter Salacia.[1] On the morning of Saturday, October 19, the convoy was spotted by U-47 commander Günther Prien, who was leading a “wolfpack” of five U-boats, having previously attacked SC.7 on the 18th. The “SC” convoy designator indicates an eastbound convoy departing from Halifax at the relatively slow speed of seven to eight knots, rather than the higher speed of the HX series.[2] Early that morning, the armed merchant cruiser detached from the convoy, but was replaced by two destroyers and three corvettes which arrived throughout the morning. Prien waited until night to launch his attack which occurred between 2100 and 0100 hours, convoy time. Fifteen torpedoes were fired, achieving 9 hits on 8 ships.[3] An additional two torpedoes were fired upon stragglers in the early morning of 20 October, for a total of ten ships torpedoed. Between the Battle of SC.7 and HX.79, all torpedoes in the wolfpack were fired,[4] which would amount to 75, assuming full stores[5]. Milner notes in passing that the magnetic pistols (detonators) on the torpedoes were not very reliable, leading a lower than theoretical kill count. According to Mawdsley’s The War for the Seas,[6] twelve ships were sunk, indicating that at least two must have been sunk solely using the deck gun. The escorts pursued the U-boats with no success.

[1] (Kindell and Hague n.d.)

[2] (Milner 2003, 43)

[3] (Kolbicz 2017)

[4] (Milner 2003, 44)

[5] (Helgason, Type IX 1995) (Helgason, Type VIIB 1995)

[6] (Mawdsley 2019, 85

Analysis of Attack on HX.79

According to Sternhell, the early U-boat attack consisted of detecting the convoy during the day, and then attacking at night with the deck awash:[1] partially submerged but with the conning tower still above the surface.[2] This lines up with Mawdsley’s description of the attack. It is generally much safer for the U-boat to attack at night, where a good number of torpedoes can be fired before the escorts can respond. Because the U-boats used the deck guns to sink at least two ships, it can be surmised that the escort force was insufficient enough to enable the U-boats to surface fully. According to Milner’s assessment of the Battles of HX.72, SC.7, and HX.79, the failure of escorts to sink U-Boats was due to inadequate escorts, who were not specialized enough for ASW work, and poor depth charges. Particularly, Milner notes that the Flower-class corvettes escorting the convoy were poorly suited to work in the North Atlantic, with short forecastles and extraneous equipment, such as minesweeping gear.[3][4]

[1] (Sternhell and Thorndike 1946, 9)

[2] (Lyman 1941)

[3] (Port Arthur Shipbuilding Co. Ltd. 1941)

[4] (Milner 2003, 45-46)

Attack on HX.228

Clay Bair’s Hitler’s U-Boat War provides a good source for the attack on HX.228. HX.228 departed Halifax with 60 merchant ships on March 5, 1943. It was defended by British Escort Group B-3, consisting of four destroyers and five corvettes, commanded by A. A. Tait in HMS Harvester. Notably, the first carrier support group, consisting of USS Bogue and two Clemson-class destroyers provided air support over the convoy’s operational area.[1]

The Allies routed HX.228 north of SC.121 to avoid U-boats that might be tailing the latter. Unfortunately, this placed HX.228 directly in the path of the German Neuland patrol. Early on March 10, Bogue sighted a submarine, but did not attempt an attack and detached to pick up survivors from S.S. Jonathan Sturges.[2] Shortly after Bogue detached, U-366, commanded by Hans Hunger, sighted HX.228. On the night of March 10-11, Neuland patrol attacked, with U-221 firing the first salvo, hitting two ships carrying ammunition, destroying them instantly. The explosion caused significant damage to U-221, preventing the attack periscope from being lowered. After diving, escorts succeeded in depth charging U-221, resulting in a serious leak. U-221 limped away for repairs. U-757 experienced a similar situation after attacking another ammunition freighter. With the help of U-119, U-757 repelled a B-24 Liberator. Throughout the night, the escorts tracked U-Boats using radar, sonar, and HF/DF[3]. Near dawn, Harvester spotted a surfaced U-444, and accelerating to full speed, rammed it. This failed to sink U-444, but the submarine was entangled in Harvester’s propellers, crippling the destroyer. U-432, seeing the crippled Harvester, fired two torpedoes, sinking it and killing Tait. French Corvette Aconit, who had been screening Harvester, sighted U-444, and as with Harvester, accelerated and rammed the submarine, this time causing it to split in two and sink rapidly. When Aconit sailed to the area where Harvester had sunk, she got a sonar contact on a submarine that turned out to be U-432, which was celebrating the sinking of harvester with Champagne. When ten depth charges were dropped on it, the Hydrophone operator was not at his station, and the submarine was unaware it was under attack. Sustaining severe damage, U-432 sunk to 1000 feet below the surface, facing certain death, the commander ordered the submarine to surface, making it the deepest diving submarine to ever surface at that point. On the surface U-432 was attacked by guns mounted on Aconit, before being rammed, sinking it. After five ships sunk (4 freighters and Harvester), the U-Boats broke off the attack, on March 11. Two merchant ships had been hit by a torpedo but did not sink and made it successfully to port for repairs.[4]

[1] (Blair 1998, 254)

[2] (US Navy Department 1945)

[3] High Frequency Direction Finding, a method of determining the location of a radio broadcast

[4] (Blair 1998, 255-257)

Analysis of Attack on HX.228

HX.228 was a successful defense of the convoy, but it could have been much more successful. Bogue spotted a submarine on March 10^th, but apparently made no effort to inform the convoy, according to the official chronology of that ship. If Bogue had informed the ships before the attack happened, the escorts would have been alert before the first two attacks landed. It appears that Bogue’s air wing attempted to sink the submarines using depth charges, but they failed to release properly.[1] According to Blair’s description of the battle, escorts were both in formation and used a combination of tracking methods to successfully locate U-Boats. U-757 repelling a B-24 Liberator, a heavy bomber, indicates that the mid-Atlantic gap had been successfully closed by March 1943.[2] Milner notes that by early 1943, the mid-Atlantic gap had largely been closed with a combination of custom designed aircraft, such as the B-24, and older aircraft designs modified for long range.[3] Closing the gap allowed for greater tracking of U-Boats and Encouraged U-Boats to spend more time submerged, limiting their range and speed. Milner also notes that radar contributed substantially to the defense of HX.228, with unusually mild weather for a North Atlantic winter improving range and effectiveness.[4]

[1] (US Navy Department 1945, 4)

[2] (Blair 1998, 255-256)

[3] (Milner 2003, 142-144)

[4] (Milner, 146)

Conclusions

The most significant change between the two battles discussed is the change in technology. Milner notes that the allied defeat in the battles of HX.79 and SC.7 indicated a need for compact radar that could be mounted on small escort ships to detect surfaced submarines.[1] Such a radar was developed in the form of the cavity magnetron, which had been invented in February 1940, but was impractical for shipboard use until late 1940 or early 1941.[2] As stated above, Milner noted the particular impact the radar had on the battle of HX.228, indicating that the technological developments substantially improved allied ASW success. Furthermore, Milner describes the development of radio direction finding as a major difference between the battles of Fall 1940 and the later ones. He notes that after finding a contact, U-Boats would make frequent radio reports to headquarters, who would instruct the U-Boats on how to attack. At the start of the war, the only direction finding were large and inaccurate shore-based installations. However, by late 1941[3], compact direction finding equipment was mounted on ships. Based on Blair’s description of the attack on HX.228, direction finding equipment played a significant role in the successes of Aconit and Harvester. Mawdsley’s research agrees with this assessment and additionally notes that the problems with small corvettes described by Milner in the context of HX.79 had largely been rectified by early 1943 with the introduction of the River-class corvettes.[4] Interestingly, no accounts of the battles discuss the impact code-breaking, which was famously important in the Battle of the Atlantic.[5] Mawdsley notes both that code-breaking was unusually ineffective around the battle of HX.228 and that the influence of codebreaking is often grossly overstated in popular perceptions of the convoy war.[6]

The role that tactics played is harder to quantify. HX.79 is certainly a failure of escort tactics. The fact that five U-Boats were able to exhaust their full torpedo complement and still sink two more ships via deck gun indicates that they attacked almost uncontested. It is noted in a 1943 U-boat Commander’s Handbook that a surfaced submarine at night is almost invisible.[7] Without radar, the escorts of HX.79 would be attacking the enemy blind, which is hardly a recipe for success. Therefore, regardless of tactics, the battle would have been an allied defeat. However, if the convoy had not split up, it is likely that the two stragglers torpedoed on October 20 would have survived. HX.228 could, in many ways, be considered a failure of tactics, especially those for early warning and proactive defenses. Despite Bogue seeing a submarine and the escorts having radar, HX.228 was unaware there were submarines in the area until ships were hit. Radar did make hunting submarines much easier, but did not prevent ship losses in the first place. The decision of A. A. Tait to ram U-444 doomed his own ship, but was tactically sound. A destroyer is significantly more likely to deal fatal damage to a submarine than itself and attempting a gun duel would result in the potential for U-444 to torpedo Harvester.

Overall, the largest factor causing the difference between the battles of HX.79 and HX.228 was technology. Radar and Radio Direction finding made it much easier to find and sink U-boats. The tactical changes between the two battles were significant, but poor communication and lack of early warning systems caused a majority of the losses in both battles.

[1] (Milner, 146)

[2] (Blanchard, Galati and van Genderen 2013)

[3] (Mason 1992)

[4] (Mawdsley 2019, 313)

[5] (Drachinifel 2020)

[6] (Mawdsley 2019, 313, 503)

[7] (High Command of the Navy 1943, Section III(A): 199-201)

Reflection

I have had a long time passion for naval history, so I used my collection of websites I had saved and my experience using the Dewey Decimal system at my local library to get a good jumping off point. From the start, I knew I wanted to do something about WWII, but I was originally planning to do something much more technical. At first I wanted to do an analysis of engineering plants on various warships, but my teacher pointed out that it would be difficult to make a good historical argument. Next, I wanted to do the impact of sonar on the convoy war, but it would be difficult to analyze such a large timescale in 2200 words. Therefore, I settled on comparing the two battles.

I selected the battles by reading some Wikipedia, always a good jumping off point. It looked like HX.79 and HX.228 were good choices because of the large number of references they had, compared to other battles, and their separation in time. I dove in, and found a great deal of sources, extensively using Google-fu to find harder to get ones. I checked out Mawdsley’s War for the Seas and Blair’s Hitler’s U-Boat War: The Hunted, 1942-1945 from my local library. I received my copy of Milner’s Battle of the Atlantic from my teacher. After extensive reading and research, which I hope is reflected in my sources, I assembled this report. Thank you for reading it.

Bibliography

Blair, Clay. 1998. Hitler's U-Boat War. New York: Random House.

Blanchard, Yves, Gaspare Galati, and Piet van Genderen. 2013. "The Cavity Magnetron: Not Just a British Invention." IEEE Antennas and Propagation Magazine 244-254.

Drachinifel. 2020. "Western Approaches Command - Fighting U-Boats with Wrens." Liverpool, England: youtube.com, June 24.

Garner, Forrest, and Ralph Hiestand. 1998. "The USS Bogue Hunter Killer Groups." uboat.net. Febuary 10. Accessed December 2022.

Helgason, Guðmundur. 1995. "Type IX." uboat.net. Accessed December 2022. https://uboat.net/types/ix.htm.

—. 1995. "Type VIIB." uboat.net. Accessed December 2022. https://uboat.net/types/viib.htm.

High Command of the Navy. 1943. "Submarine Commander's Handbook."

Kindell, Don, and Arnold Hague. n.d. "HX CONVOY SERIES: Convoy HX.79." convoyweb.org.uk. Accessed December 2022.

Kolbicz, Rainer. 2017. Re: British S/S Wandby and Ruperra in convoy HX-79: Warsailors.com. September 2016. Accessed December 2022.

Lyman, Henry. 1941. "World War: A survivor Talks." Time, November 10.

Mason, Geoffry B. 1992. "HF/DF or HUFF DUFF - HIGH FREQUENCY RADIO DIRECTION FINDING in ROYAL NAVY WARSHIPS." naval-history.net. Accessed December 2022. https://www.naval-history.net/xGM-Tech-HFDF.htm.

Mawdsley, Evan. 2019. The War for the Seas. Yale University Press.

Milner, Marc. 2003. Battle of the Atlantic. St. Catharines, Ontario: Vanwell Publishing Ltd.

Niestle, Axel. n.d. "Convoy HX 79: Cruising Order and Notes." warsailors.com. Accessed November 2022.

Port Arthur Shipbuilding Co. Ltd. 1941. "General Arrangement: Corvette Hulls 51-58." Ontario, November 19.

Sternhell, Charles M., and Alan M. Thorndike. 1946. OEG Report No. 51: Antisubmarine Warfare in World War II. Washington, D. C.: Operations Evaluation Group.

US Navy Department. 1945. "Chronology of the USS Bogue."