The Longest Time a World War II Submarine Could Stay at Sea Without Resupply

The enduring legacy of World War II includes a myriad of technological advancements and innovative strategies, including the capabilities of submarines. Among the most fascinating is the question of how long a submarine can stay at sea without resupply, a critical factor in their operational success during the conflict.

Japanese I-400 Submarines: Pioneers in Endurance

At the height of World War II, the Japanese developed the I-400 class submarines, which were designed with unprecedented range and endurance. These vessels were capable of staying at sea for up to 100-120 days without resupply, thanks to advancements in propulsion and fuel efficiency. The I-400 class, while extremely impressive, entered service too late to fully leverage their potential, and only a few units were completed before the war's end.

German Type IVD2 Submarines: Champions of Long Ranges

Additionally, the German Type IVD2 submarines also boasted remarkable endurance and range, with a home range of 23,700 nautical miles and supplies for 84 days at sea. In certain circumstances, through the use of rationing and occasional fishing, the endurance could be increased to 90-95 days. The record for the longest war patrol was set by U-196, a Type IXD2 submarine, which completed a 225-day patrol, from March 13, 1943, to October 23, 1943. During this voyage, the submarine visited the Indian Ocean, attacked two British ships, and returned home without refueling or resupplying at sea. Interestingly, it is believed that the submarine may have received some supplies during the journey, which further extended its range and endurance.

US Tench-Class Submarines: Ranges and Endurance

On the other side of the Atlantic, the US Navy also operated submarines with impressive range and endurance. The Tench-class submarines had a range of 16,000 nautical miles and carried supplies for 75 days on board. While these figures were impressive, they were still surpassed by the Japanese Type C mod submarines, which had a range of 21,000 miles and carried fuel for about 70 days.

The USS Barb: A Record-Holding War Patrol

Notably, the USS Barb performed a 75-day war patrol, which might be the longest recorded for a U.S. submarine. It is also the only submarine to 'sink' a Japanese train, a significant feat in the context of World War II. Such endurance was crucial for the operational success of these submarines, particularly for missions that required extended periods of operation without resupply.

United States Submarines: Averages and Regular Transits

Regarding U.S. submarines, my estimation, based on patrol reports, is that the average duration of a patrol was around seven weeks. This included a two-week transit from Pearl Harbor to empire waters, two to three weeks on station, and a two-week return journey. Only a small fraction of this time was spent submerged. It's important to note that these voyages were often preformed with the knowledge of where the submarines were, as the Allies had cracked the U-boat codes and developed advanced radar technology.

Between 1939 and the end of 1941, before the advent of effective codebreaking at Bletchley Park, the Allies used "Milch Cows," large submarines that would refuel and resupply torpedoes to ensure U-boats remained operational. Additionally, Spanish and Portuguese waters, particularly the Canary Islands, served as essential resupply points for U-boats, with British forces sinking these resupply ships in neutral waters.

Long Voyages and Refueling Stops

Long range voyages, such as those targeting the East coast of the United States in 1942, involved trips of up to 10,000 nautical miles. These ventures often left the submarines low on fuel, necessitating refueling stops at the Canaries. After 1942, the Allies became increasingly adept at tracking and sinking U-boats due to cracked codes and new radar technology, making long-range missions more perilous.

Conclusion

The enduring record of submarine capabilities during World War II is a testament to the ingenuity and innovation of naval engineering. The ability of submarines to stay at sea for extended periods without resupply was critical for their success in the war. The I-400 class, German Type IVD2, U.S. Tench-class, and even the USS Barb set benchmarks that remain mysteries to naval historians and enthusiasts today. The data and records of these operations continue to fascinate and inspire, offering valuable insights into the history of naval warfare.