Owing to the technical difficulty of building an ELF transmitter, the U.S., China, Russia, and India are the only nations known to have constructed ELF communication facilities. Until it was dismantled in late September 2004, the American "Seafarer", later called "Project ELF" system (76 Hz), consisted of two antennas, located at Clam Lake, Wisconsin (since 1977), and at Republic, Michigan, in the Upper Peninsula (since 1980). The Russian antenna ("ZEVS", 82 Hz) is installed at the Kola Peninsula near Murmansk. It was noticed by the West in the early 1990s. The Indian Navy has an operational VLF communication facility at the INS Kattabomman naval base to communicate with its Arihant class and Akula class submarines. Beginning in 2012, this facility was being upgraded to also transmit ELF communications. China on the other hand has recently constructed the world's largest ELF facility roughly the size of New York City in order to communicate with its submarine forces without them having to surface.