The Lethality of Deck Guns on Submarines During WWII: Largest Ship Sunk by a Sub's Gun

The deck gun, a crucial weapon for WWII submarines, played a significant role in engagements where torpedoes were in short supply. During the wars, the deck gun served as a fallback option for sinking merchant ships with minimal defensive capabilities.

The Key Role of Deck Guns in WWII

WWII submarines were constrained by the limited number of torpedoes they carried. For instance, the German Type VII U-Boat carried 14 torpedoes, while the larger Type IX had 22. The limited supply of torpedoes often dictated the range and accuracy at which they could be fired. Many captains chose to conserve torpedoes for more certain hits, making the deck gun a viable alternative.

Effectiveness of Deck Guns

Deck guns offered submarines a means to attack merchant ships at relatively close range, a critical advantage given the primitive nature of torpedoes at the time. The USS Yorktown, for example, was sunk by a Japanese submarine after taking significant damage from bombing and torpedo hits. The deck gun became the final straw that led to her sinking.

A Successful Gun Captain: Lothar von Arnauld de la Perière

Lothar von Arnauld de la Perière, one of the most successful submarine captains in history, sank 194 ships totaling 453,000 tons. A significant number of these sinkings were achieved using the deck gun alone. The ease of hitting water line targets from close range made the deck gun a preferred weapon, especially during the early stages of the war when submarines and torpedoes were less advanced.

Strategic Use of Deck Guns

The strategic importance of the deck gun became less significant as the Allies improved their anti-submarine warfare measures. By the later stages of the war, merchant ships were better equipped with defensive armament, and convoys were more prevalent, reducing the efficacy of deck gun attacks. This shift led to the removal or replacement of deck guns in many U-boats.

Highly Unusual Surface Engagement

A notable exception to the waning use of deck guns during WWII was the engagement between the destroyer USS Borie and the German U-boat U-405. On November 1st, 1943, USS Borie depth charged U-405, driving it to the surface. The sub's crew attempted to engage the destroyer with its deck gun, but USS Borie's AA and surface guns neutralized the threat, and the sub was eventually sunk. This engagement underscores the rare but possible outcome when submarines surface and engage ships from very close range.

Case Study: Largest Ship Sunk by Deck Gun

The largest ship sunk by a submarine's deck gun during WWII is difficult to ascertain due to the lack of detailed records. Thousands of merchant ships were sunk, making it a painstaking task to determine the largest one sunk by a deck gun. However, a notable example is the SS Cynthia Olson. This 1919 vintage cargo ship, carrying lumber from Tacoma, WA, to Honolulu, was sunk on December 6th, 1941, by the Japanese submarine I-26. The ship was hit by 47 shells, causing it to sink.

The Cynthia Olson is significant not only because it was the first US merchant ship lost during the war but also because it illustrates the effectiveness of a deck gun in sinking a ship engager and its crew.