How Did WWII Submarines Deal with Mines?
In the early stages of World War II, submarines faced significant challenges when it came to navigating through minefields. Since most submarines were unable to detect mines using sonar until later in the war, they were effectively blind while submerged, posing a significant risk to their operations.
Royal Navy's Early Anti-Sub Minefield
The Royal Navy employed an innovative strategy at the beginning of the war by laying an anti-sub minefield in the Strait of Dover. This minefield, which covered varying depths, was highly effective in the first few months of operation. The Germans, who had to navigate this obstacle, lost three U-boats on these mines within a short time frame. As a result, German efforts to enter the Channel were significantly hampered until May 1940.
Submarine Losses to Mines
Despite the initial success of the Royal Navy's tactic, submarines were not immune to the dangers of mines. Some were lost due to the unknown risk lurking in the water. Later in the war, the U.S. Navy made significant advancements in mine detection technology. In particular, the development of a high-frequency short-range FM sonar allowed US submarines to successfully operate in areas such as the Sea of Japan.
Types and Use of Sonar
Sonar technology has a long history, but most people think only of active sonar when considering the technology. However, there are fundamentally two types of sonar: active and passive. Active sonar emits sound waves and detects the echoes to map out items and structures underwater, while passive sonar collects ambient sounds and uses them to make the same determinations. Passive sonar offers better stealth capabilities but is less effective than active sonar in certain situations.
Before the advent of sonar, early submarines used a long nose spar to 'feel' what was ahead and could even attach explosive charges to the hulls of surface vessels.
Modern Fishing Traps and Radar Technology
With the advent of sonar and radar, mines would appear as blips on the radar screen, simplifying detection and navigation. However, before these technologies, submarines had to rely on physical methods to detect mines. The best strategy was usually to stay below the depth at which the mines were moored, particularly if they were not free-floating. When surfaced, submarines would be more like other vessels, requiring lookouts to spot mines.
US Navy's Mine-Detecting FM Sonar
Later in WWII, some US submarines were equipped with high-frequency short-range FM sonar, designed for inshore operations in the Sea of Japan. This development provided a significant advantage in mine detection, but the technology was not available to all submarines. Besides, there were some reservations among the crews, as documented in Clay Blair's "Silent Victory." The FM sonar was not well-received, and crew signs reading "Is this journey necessary" were displayed in protest against the use of the sonar, often in reference to gas rationing slogans of the time. The end of the war intervened before a final resolution could be reached.