To equip US Army Air Corps planes, the US Army adopted in 1941 a reduced set of radios from the ARA/ATA range. Designated SCR-274-N, these Army radios were electrically almost identical to their ARA/ATA counterparts, except for receiver output and modulator sidetone audio transformer output impedance. Structurally and in appearance, they were virtually identical except for most later units being left unpainted aluminum in contrast to the black wrinkle finish of the Navy sets. The designation SCR-274-N is a pre-World War II Army equipment nomenclature. The Army never acquired the ARA 1.5 to 3.0 MHz receiver, nor the ATA 2.1 to 3.0 MHz transmitter. Initially, it did not acquire the 3.0 to 4.0 MHz transmitter, nor the 0.52 to 1.5 MHz receiver, but the need to communicate on the common civil airfield frequency of 3.105 MHz plus the anticipated USAAF use of the AN/ARR-1 homing adapter (see below) compelled adding these units to the SCR-274-N. Early Army units were made by Aircraft Radio Corporation, but the vast majority was made by Western Electric, plus a few by Colonial Radio and others.