presented by:
Omer Tolga Inan

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1. Foreword
The Second World War marked the birth of modern day technological warfare; innovations of well-educated scientists and engineers trumped the brute power of well-trained, disciplined troops. Among the most vital of these innovations were those spearheading the advancement of submarine technology in the critical quest for control of the sub-Atlantic: discoveries in very low frequency (VLF) transmission allowed for submarine to submarine, shore to submerged submarine and submerged submarine to shore communication; novel high frequency direction finding (HF / DF) and ultrasonic / radio detection methods provided accelerated, accurate spatial localizing of submarines; and significant revelations in shipboard battery power management greatly increased the maximum time duration for which submarines could remain submerged. The conjunction of these discoveries in communication, localization, and power management coined a much more effective and powerful means of underwater warfare which was unimaginable prior to World War II. This report supplies a brief history of naval technology, a description of each of these important advances in the war of the sub-Atlantic and, introduces some aspects of modern day naval communication systems.
2. Brief History of Naval Technology
The early part of the 20th century was laced with important naval technological advancements in several fields including the induction of shipboard radio communication systems, invention and progression of vacuum tube radio equipment, and introduction of aircraft receivers. Each of these three major developments contributed significantly to the naval technological boom during World War II, and each is broadly discussed below.
2.1 The Dawn of Radio Communications
In the late 19th century, the U.S. Navy recognized an increasing need for advancement in the field of communication between Central Command in Washington and various vessels stationed around the world. Consequently, they showed distinct interest in the newborn success and practicality of radio communication. They deduced that rapid wireless communication between stations on shore and ships at sea was a very attractive prospect as it could significantly expand the tactical and strategic capacity of the U.S. Navy. This reasoning led to a close and careful surveillance of Guglielmo Marconi’s presentation of his radio equipment at the International Yacht Races of September 1899, and the subsequent adoption of this equipment aboard the USS New York. On November 2nd, 1899, the USS New York transmitted the first “official” naval message to Navesink, NJ in a call for refueling. This marked the beginning of naval radio communication.
2.2 Early Vacuum Tube Equipment and the Era Preceding Transistors
The vacuum tube was invented in 1906 by Lee DeForest and almost completely replaced its predecessors, the arc and spark transmitters, by World War I. This substitution was on account of significant advantages of the vacuum tube, including its ability to provide a cleaner, more efficient, single frequency signal ideal for radio transmitters and receivers. However, these advantages were not immediately apparent to DeForest in 1906 as his original intent was to detect radio waves and convert them to audible sounds. In fact, it was not until 1911 before he showed that the “audion” (three-element vacuum tube) could amplify signals, and 1913 before he demonstrated oscillations. These two discoveries were, of course, essential to the audion’s future as the building block for radio.
The next significant furthering of the audion was in 1914 when Edwin Howard Armstrong caused it to oscillate at higher frequencies that allowed for feedback, and, subsequently, world-wide wireless communication. One year later, as a result of this development, the U.S. Navy communicated by voice from Virginia to Paris, California, and Hawaii. The success of the vacuum tube was official, and the technology was fully adopted by the Navy before and during World War I.
2.3 Aircraft Transmitters and Receivers: Radio in the Sky
Aircraft radio became an effective reality at the close of World War I when a naval radio group devised radio shielding to significantly improve reception of two-way communications. This method involved preventing radiation from the engine ignition system, including spark plugs, cables, and other devices, from escaping and interfering with the radio waves. Metallic conductors encompassed the engine components, thus reflecting and internalizing the electromagnetic radiation. The result was remarkable radio reception and a wide open door for the first aircraft radio-communication equipments in 1922. 2
3. Naval Technological Innovations of the Second World War
The Allied troops and the Germans were involved in a sub-Atlantic chess match during World War II that played a crucial role in determining the outcome of the war. In this battle, technological advances became a requirement for survival, and a prerequisite for victory. Very low frequency communication, spatial localizing, and power management were three of these advances that were most consequential in the development of this sub-Atlantic war and are discussed below.
3.1 The Art of Underwater Communications
Underwater transmission problems are common in most undergraduate electromagnetic wave theory textbooks since they involve many of the fundamentals of wave propagation through lossy media. Additionally, these underwater transmission problems are at the heart of understanding motivations for very low frequency transmission in submarine communications. However, to be able to technically examine the technologies implemented during World War II, one must first become familiar with basic electromagnetic wave theory. This section introduces fundamental wave propagation concepts in general and for the specific case of seawater transmission, then discusses an important World War II application: the German Goliath Antenna.
3.1.1 Brief Introduction to Electromagnetic Wave Theory
Fundamental electromagnetic wave theory asserts that a wave traveling in any medium will propagate and attenuate at different distances based on the properties of that medium. The characteristics of the medium that are of interest in determining the degree of attenuation are the permittivity, permeability and relative conductivity. Once these constants are known, one can use the following mathematical relationship to determine the “skin-depth” in the medium, defined as the distance at which a traveling wave attenuates to
approximately 37% of its initial intensity: ______
δ = 1 / α ≈ 1 / √ π f μ σ
In this equation, δ is the skin depth, α is the attenuation constant, f is the frequency, and μ and σ are, respectively, the magnetic permeability and the conductivity of the medium. It is also clear from this relation that the skin-depth is a function of frequency of the wave. In fact, it is inversely proportional to the square root of frequency. This is the primary motivation for very low frequency transmission: in media where the skin depth is low for high frequency waves, it will be much larger for lower frequencies. Seawater is a perfect example of this type of medium.
3.1.2 Electromagnetic Characteristics and Calculations for Seawater
Seawater has a conductivity, σ, of 4 S/m (Siemens/meter), relative permittivity, εr , of 81, and relative permeability, μr , of approximately 1. Using these parameters one can find that seawater is a “good conductor” of electromagnetic energy for frequencies lower than approximately 800 MHz. Additionally, using the equation described in the previous section, one can determine that the skin depth of seawater is on the order of centimeters at 10 MHz while on the order of meters at 10 kHz. A complete plot of skin depth versus frequency for seawater is provided in Figure 1 below. An interesting exercise from Inan and Inan’s text, Example 2-11d, is the calculation of the minimum electric field amplitude required for communication with a submarine capable of receiving electric fields of 1 μ V / m or greater submerged 100 m underwater.4 The resulting magnitude is 2.84 kV / m, a very realistic value for several World War II transmitters including the German Goliath Antenna