[Milsurplus] wire question

[elden meyer]

I have been working on a Collins 51Y4 ADF receiver (R-1391/ARN-83).
The chassis wiring seems to be copperweld, i.e. copper plated steel,
rather than copper conductors. Looks to be about 26 AWG stranded 
and has the typical silver plating and Teflon insulation.

I've seen steel wire in really cheap import stuff, but surely Collins was not
being cheap. Was this to get adequate mechanical strength in a small
diameter? Was/is there any other usage of copperweld hookup wire?