I was at the Museum of Flight in Seattle, WA, yesterday, and came across a Blue Angel aircraft, pictured below.
Along the right front of the plane, there is a small tube that is capped with a silver cap.
I thought at first that this might be a refuelling point, but (A) I didn't see any real purpose to have mid-air refuelling on a Blue Angel, and (B) it doesn't seem like a great place to refuel (since it seems like it could easily obstruct the pilot's view).
(I looked online at some images of Blue Angel aircraft and realized there are several makes. However, I didn't find this particular tube and cap on any of the other makes. (example) In fact, I don't even recall what make of Blue Angel this craft actually is.)
What is this tube at the front of the jet, and what is it used for? Why does it only appear on some makes of the jet?