Hellcats by Peter Sasgen Read Free Book Online Page B

used a then-new audio technique designed for commercial radio broadcasting called frequency modulation. Unlike AM, or amplitude modulation broadcasts, in which the audio carrier wave frequency is constant, the FM audio carrier wave varies in frequency. Conventional sonar units of the 1940s used a short pulse of sound transmitted on a constant frequency followed by a long silence as the return echo from a detected object was converted into an audible sound on the same frequency. By contrast, FM sonar emitted a steady, continuous signal modulated to avoid interference between the outgoing signal and the returning echo from a detected object, thus ending the requirement for a time lag. The experimental unit Harnwell demonstrated could locate submerged objects of every description, including shoals, sandbars, kelp, steel submarine nets, and even steel-hulled ships. In an earlier test it had even detected dummy mines. Realizing that such a device would interest Lockwood, Dr. Henderson explained that though FM sonar was originally developed for use by minesweepers, it could also be used by submerged submarines to plot a course into a defended enemy harbor.
    Though Lockwood was impressed with Harnwell’s and Henderson’s Alice in Wonderland invention, he didn’t see how the device could be used by a submarine. At that time submarine targets were concentrated in deep-ocean areas of the Pacific where an attacking sub had room to maneuver and to evade Japanese escort vessels. The harbors where Japanese ships sometimes took refuge from attack were in most cases too shallow for submarines to enter without being detected, even if they had a device that could plot a course into and out of a harbor, so it wouldn’t make any difference. For Lockwood, FM sonar was an interesting gadget that not only proved the scientists at UCDWR were inventive, but also that the Navy’s substantial financial investment in the lab was starting to pay off.
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    Lockwood returned to Pearl Harbor buoyed by what he saw at UCDWR but disappointed by the long gestation period needed to develop the devices and to manufacture them in quantity for use by the sub force. Nevertheless, he reckoned that with his visit to UCDWR the force had established one of its most valuable contacts with the scientific world, and with Harnwell and Henderson, who would later play major roles in future submarine operations. After writing a report on his trip for distribution to Admiral King, Admiral Nimitz, and his own immediate staff, Lockwood put aside what he’d learned in San Diego for more pressing matters. At the top of his list was the get-acquainted look-see patrol of the Sea of Japan by a task force of submarines.
    Lockwood wasn’t sure what to expect from such a mission. He knew that Japanese ships were plying their routes in the Sea of Japan, carrying essential cargoes of food and raw materials back to mainland Japan. The big question was, How many ships were actively involved in this work, given that the bulk of the empire’s merchant marine was busy elsewhere in the Pacific? How plentiful would targets be in the Sea of Japan? Would there be enough to justify the risks entailed in sending a couple of subs up there on a raid? He and Voge wouldn’t know until they tried it. Furthermore, if submarines suddenly showed up in the emperor’s sea, would the Japanese rush to block its exits, trapping the subs inside until they ran out of food and fuel, to be hunted down and sunk? Lockwood mulled these questions over for a time, then decided that the risk was worth taking, if for no other reason than it would provide the Navy’s high command with vital information on the state of Japanese resupply operations at home. That information might influence future planning for an invasion of Japan, which would likely be necessary to end the war.
    To avoid a prolonged operation in the Sea of Japan that would give the Japanese time to mount an