The fact that AM broadcasting has lasted this long before declining is pretty amazing. One of the original pioneers of broadcasting, Edwin Armstrong, predicted and lobbied to move away from AM back in 1933. In 1933 Armstrong took out four patents on FM and presented David Sarnoff and RCA with his invention, hopeful that his friend would take the lead in promoting the revolutionary new medium. That same month RCA announced its allocation of $1,000,000 for television tests.” TV was the new rage; nothing more about FM was forthcoming from RCA for another four years. Armstrong was angry over being induced to waste his time by a company that had no interest in developing his invention.
Determined to show the value of FM, Armstrong asked the FCC for spectrum space for further FM experiments and sought permission to build his own station. At hearings in 1936, Sarnoff confirmed Armstrong’s suspicions. He testified against allocating space to FM and urged that it be given to television instead. The company stood to keep a greater share of any profits to be made from television than from FM radio. Moreover, since it was a vastly superior radio service, FM represented a threat to established AM operations—in which RCA, as the parent company of the NBC network, had made great investments.
Regarding the use of VLF or HF for communicating with submarines? You do realize the baud rate that is used for VLF is something like 5-baud. Anymore subs release a satellite communication buoy for timely messages. Therein is another problem with using VLF, HF, or MW for digital communications. Beside the propagation, terrestrial (impulse) noise, and the amount of power required for long distance communication, we're talking Hertz or Kilohertz here folks. Modulated bandwidth capabilities just aren't up to modern needs.