In 1944, the growing U.S. production of war materiel for the Allies resulted in an increasing need to rationalize the peripheral device schema used by different countries in order to be able to better use the equipment across the military forces of those countries. One of these areas was the use of aircraft microphones. British aircraft used dynamic microphones with a lower output level than the USAAF, which depended for the most part on the use of carbon microphone elements in their aircraft equipment. Adding to this mix was the onset of production of a couple of different oxygen mask microphones for U.S. and British aircraft (T-34 and T-44) that improved intelligibility over the old carbon microphone elements, according to Bell Labs tests. Some transmitters like the AN/ART-13 had dynamic microphone capabilities designed into them, but not all equipment had dual compatibility. Those factors required the reintroduction of a device that had not been in the US inventory since the mid-1930s (the BC-216), when a USAAC evaluation of dynamic microphones (in an ill advised throat microphone configuration) ended in favor of carbon phone element technology, primarily for economic reasons. The Packard Bell Model K (1944) and K-1 (1945) filled the resulting gap well, operating on 28vdc without requiring a dynamotor supply. The K-1 added a level adjustment pot to the front panel to better accommodate different microphones.