Radio Altimeter Altitude Limit Selector Switch, SA-1/ARN-1 for AN/APN-1 P-63 the differential pressure being indicated

the differential pressure being indicated by the gap between the two pointers along the index

The metal seal is in place in the lower right of the case

part number 3416-3A-A1

clearly made for an Air Corps order

Radio Altimeter Altitude Limit Selector Switch, SA-1/ARN-1 for AN/APN-1 P-63 the differential pressure being indicatedThe WWII era Radio Altimeter Altitude Limit Selector Switch, SA 1 ARN 1 was a component of Radio Set AN APN 1, used to measure and indicate to the pilot the altitude over the terrain during flight. See image of spec sheet. The Radio Altimeter was used in a number of aircraft of the US Navy where close monitoring of height over terrain was critical, such as torpedo bomber TBM Avenger (see image from TBM Flight Manual), dive bomber SB2C Helldiver,