On Fri, 30 Mar 2018 10:10:43 -0400, Peter Stickney
wrote:

... it was hull number 5 in the initial run of the
prototype A series (X-11) Atlases, and, as a static test article, wasn't
flown.
So, it's Atlas A, #5.
16 Atlas As were built, and 8 were flown (to varying degrees of success)


Thanks for filling thst in.