In typical WIX fashion, no one has actually attempted to answer the gentleman's original question. I guess I'll take a stab at it.
Army aircraft were usually equipped with some version of the SCR-274N "command" radio equipment, which operated in the 3.0 to 9.1 MHz range (individual transmitter units covered 3.0 - 4.0, 4.0 - 5.3, 5.3 - 7.0, 7.0 - 9.1 mc, and individual receiver units covered 3.0 - 6.0 and 6.0 - 9.1 mc, as well as a 190 - 550 kc unit for beacon reception).
Navy aircraft were usually equipped with some version of either the ATA or AN/ARC5 "command" radio equipment, which operated in the 2.1 to 9.1 MHz range (individual transmitter units covered 2.1 - 3.0, 3.0 - 4.0, 4.0 - 5.3, 5.3 - 7.0, 7.0 - 9.1 mc, and individual receiver units covered 0.5 - 1.5, 1.5 - 3.0, 3.0 - 6.0, and 6.0 - 9.1 mc, as well as a 190 - 550 kc unit for beacon reception). ATA was an earlier set, and AN/ARC5 came later. Both were used throughout WW2.
In both the Army and Navy applications, "command" sets were used to communicate with the control tower while on the ground or in the pattern, and were used to communicate between aircraft while in flight. Being HF units, wire antennas were the order of the day. Large aircraft were usually equipped for multiple bands, while smaller aircraft might only be equipped for one band. In most cases, the transmitter, modulator, and receiver unit(s) were mounted remotely with local control units installed in the cockpit and/or radio operator's station.
All of the above radios are often referred to by restorers and ham radio operators as "Arc Fives", but that moniker is only correct for the Navy's AN/ARC5 units. Though the Army and Navy radios look almost identical and cover very similar frequency ranges, they are not interchangeable because of differences in connectorization. There are also minor differences in the internal circuitry, especially in the transmitters. The Navy ATA and AN/ARC5 components are also not directly interchangeable, also because of differences in connectorization.
Later in the war, the Army adopted the British-developed VHF radios for "command" purposes. VHF worked better for short-range communications and the radio waves don't tend to travel long distances like HF signals do.
Plenty of information is available on the internet (Google is your friend!). Now that you know what to look for, you can overdose on radio info!