Friday, June 2, 2023

    What is the maximum duration a WW2 U-Boat could remain submerged?

    World War II marked a significant advancement in naval warfare technologies, particularly for German U-Boats, which were the most feared enemy submarines during the conflict. U-Boats posed a significant threat to Allied shipping and became instrumental weapons of war. However, being submarines, a major question that arises is, how long could a World War II U-Boat remain submerged? This article delves into the limits of WWII U-Boats, exploring their design, capabilities and the reasons they needed to resurface so frequently.


    The German U-Boats were primarily designed as attack submarines, with a focus on stealth and a range of operational features including torpedoes and deck guns for both surface and underwater engagements. Most WWII U-Boats were designed to function relatively close to the surface for a considerable part of their operations.

    One primary factor determining the maximum submerged duration of a WWII U-Boat is the type of propulsion system it used. The majority of WW2 U-Boats were powered by diesel engines and electric motors. The diesel engines were used when the boat was surfaced or snorkeling (using an air intake snorkel). These engines could not run while submerged since they require oxygen to operate, meaning they would deplete the air inside the boat and produce dangerous levels of carbon monoxide.

    Submerged Propulsion

    While submerged, the U-Boats switched to their electric motors, powered by a massive battery bank. The electric motors allowed silent running, virtually undetectable by surface vessels, making them deadly predators. However, the battery capacity was limited, and it affected the U-Boat’s maximum speed, operational range, and most importantly, the amount of time it could remain submerged.

    Battery technology in the 1940s was limited compared to modern standards, so most WWII U-Boats could not stay submerged for extended periods without surfacing for additional charging. Generally, U-Boats would recharge their batteries overnight, when darkness offered the cover needed to minimize the risk of enemy detection.

    Maximum Submerged Duration

    The maximum submerged duration of a World War II U-Boat varied depending on the type of U-Boat and the specific conditions of each mission. The most common U-Boat during the war, the Type VII, could remain submerged for up to 24 hours at a slow speed of about 3 knots. In comparison, the slightly larger Type IX U-Boat could stay submerged for up to 72 hours at a similar speed. However, these figures were in ideal circumstances, and various factors such as damage or failures in the onboard systems could significantly reduce the submerged time.

    The Need to Surface

    In addition to the need to recharge their batteries, there were other reasons why WWII U-Boats needed to resurface frequently. First, the submarine’s crew needed fresh air, as the boat’s closed environment led to carbon dioxide buildup and other impurities. Moreover, the boat’s diesel engines also needed air to run, essential for battery recharging as well as propulsion when the submarine was surfaced or snorkeling.

    Another reason WWII U-Boats needed to surface was to replenish their food and water supplies for their crew. While some food provisions could be stores for long periods, fresh water was a limited resource on board.

    The maximum duration a World War II U-Boat could remain submerged depended on the type of U-Boat and its specific circumstances. While submarines like the Type VII and Type IX U-Boats could stay submerged for 24-72 hours, it was often practical to surface regularly for battery recharging, fresh air intake, and replenishing supplies. These time limitations were dictated by the technological constraints of the era and affected their stealth capabilities, as well as the tactics employed during the conflict. Despite these limitations, WWII U-Boats proved to be formidable weapons, contributing to the significant advancements in submarine technology witnessed throughout the war, many of which continue to influence naval warfare to this day.

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