Gabe, you don't need to keep posting card pictures. I think everyone knows what missiles do.
As for missile turrets...not on a small ship.
Five seconds on Google told me all I needed to know about "Red Jammer". Emphasis mine:
[...] the Red Y-Wing Studio Model was never seen onscreen. It was speculated to have been the first Y-wing built for Star Wars-A New Hope, but that has yet to be confirmed. The term “Red Jammer” was applied to it via the modeling world as a referral to it and the name simply stuck.