possibly to Kreger Company of California. In the late 1940s the Air Force assumed control of the Haiku and Marion, Massachusetts facilities. The Air Force found that longwave transmissions were more reliable than shortwave when sending weather information to Arctic researchers as well as bases in Greenland, Labrador, and Iceland. The two Marion transmitters were used until 1957. One was scrapped in 1961 and the other was reportedly handed over to the U.S. Bureau of Standards and stored in a Smithsonian Institution warehouse. Design The Alexanderson alternator works similarly to an AC electric generator, but generates higher-frequency current, in the very low frequency (VLF) radio frequency range. The rotor has no conductive windings or electrical connections; it consists of a solid disc of high tensile strength magnetic steel, with narrow slots cut in its circumference to create a series of narrow "teeth" that function as magnetic poles. The space between the teeth is filled with nonmagnetic material, to give the rotor a smooth surface to decrease aerodynamic drag. The rotor is turned at a high speed by an electric motor through a speed–increaser gearbox. The machine operates by variable reluctance (similar to an electric guitar pickup), changing the magnetic flux linking two coils. The periphery of the rotor is embraced by a circular iron stator with a C-shaped cross-section, divided into narrow poles, the same number as the rotor has, carrying two sets of coils. One set of coils is energized with direct current and produces a magnetic field in the air gap in the stator, which passes axially (sideways) through the rotor. As the rotor turns, alternately either an iron section of the disk is in the gap between each pair of stator poles, allowing a high magnetic flux to cross the gap, or else a non-magnetic slot is in the stator gap, allowing less magnetic flux to pass. Thus the magnetic flux through the stator varies sinusoidally at a rapid rate. These changes in flux induce a radio-frequency voltage in a second set of coils on the stator. The RF collector coils are all interconnected by an output transformer, whose secondary winding is connected to the antenna circuit. Modulation or telegraph keying of the radio frequency energy was done by a magnetic amplifier, which was also used for amplitude modulation and voice transmissions. The frequency of the current generated by an Alexanderson alternator in hertz is the product