[Milsurplus] IFF vs. ARR

[William Shinko]

(Sorry for the resend - previous email modified by mail provider)

A few weeks ago I purchased a B-29 Flight Operating 
Instructions manual reprint ( AN 01-20EJ-1, 25 Jan 1941) 
at the Columbus airshow at Rickenbacker field. In looking 
at the radio gear reportedly installed in the '29, the text
and drawings mention the IFF equipment as being the SCR-
535A, SCR-595 or SCR-695 and there is some basic info for 
its operation (really no more than how to turn it on and 
off). 

The thing that caught my eye is that the manual also shows
an SCR-515A (BC-645) installed as the "A.R.R. Radio" 
but there's nothing at all said about its purpose or how
to use it.

I'm not familiar with the ARR designation; from what I've 
read I thought the SCR-515A was a MK IV IFF that was 
developed in the early forties but wasn't put into 
widespread service. Can someone tell me what the 
"A.R.R." acronym means, and why the B-29 might show both 
units being installed (especially if the MK IV was not 
generally deployed)? Do you think that the omission of 
operational information about the A.R.R. Radio was 
intentional or an oversight?

Thanks,
Bill WB8KTA





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