Examination of wartime Argus Eyes issues suggests that Bendix radio compass equipment, primarily the control boxes for Bendix radio compasses, comprised a large fraction of Argus’s wartime radio production. There are two relatively complete radio compass systems in the exhibit, the SCR-269 and the MN-26. The SCR-269 was the most common radio compass on American bombers during the war. The MN-26 was used before and during the war on both military and civilian transport aircraft.

A radio compass is basically a radio receiver connected to a directional antenna. It allows the navigator to determine the direction of a distant transmitter. A second bearing to another transmitter allows the aircraft’s position to be determined. The MN-26 system requires the pilot or navigator to manually adjust the direction of the antenna. The SCR-269 system includes circuits in the BC-433 receiver that direct the antenna toward the tuned transmitter. This classifies it as an automatic radio compass.
The SCR-269 area in the exhibit includes the BC-433 receiver and its BC-434 control box. The latter is documented in both Argus Eyes and the 1946 Argus report. The BC-433 band switching motor (an internal component) is also shown in the 1946 report.

The LP-21 is the loop antenna (in its teardrop housing) used in the SCR-269 system. The LP-21 helps give scale to the model of the “Teggie Ann,” the fated lead bomber on the August 1, 1943 raid on Ploesti, Romania. The LP-21 is the tiny black teardrop toward the back of the top edge of the Teggie Ann’s fuselage.

The Ploesti raid, “Operation Tidal Wave,” was a low-altitude, daylight run, and the Teggie Ann was using visual navigation, not its SCR-269 system, when it turned toward Bucharest rather than continuing on course toward Ploesti. The error was due to taking the wrong branch of a railroad line that was used to guide part of the course.