Gordon Odegard had an article in the September 1965 MR showing the large spark arrestors on Milw Rd E units, and the photos show them to be well weathered.
There were other spark arrestors such as heavy screening over exhaust pipes and such that I have seen in various books but these were big retro-fit items.
Dave Nelson
I honestly have no idea, but I suspect if you look at some photographs of MILW locomotives which give the date they were taken (or even just year or decade) you can get a pretty good idea of when MILW began wide spread use of such spark arresters.
If this answer isn’t helpful enough perhaps another forum member will notice this thread when I bump it to the top!
Regards, Isaac
I model my railroad and you model yours! I model my way and you model yours!
When did the Milwaukee Road start using the large roof mounted spark arrestors on their non-turbo locomotives?
Modeling BNSF and Milwaukee Road in SW Wisconsin