Imitating the sound of a freight train whistle seems to be an obligatory part of all blues players’ vocabulary. For this purpose Mark Knopfler often uses a particular chord, a chord that appears on songs like Eastbound Train or Gravy Train (live), but also on the The Bug.
The chord in question is often called a 6/#9 chord (sometimes also denoted as 6/10). Remember, the numbers indicate the interval from the root note, so it is a chord with the 6th scale note added, and the sharp 9th note.
In C the 6th note is an A, the 9th is a D, but here we have a sharp nine, which is a half note higher, a D# (or Eb if you see it as 6/10 chord).
So our C 6/#9 would be (e.g.): C, E, G, A, D#
As a guitar player you probably want to leave out one or the other note (we only have 4 left-hand fingers), so we might get e.g. : C, G, A, D#
The following diagrams shows how to play these notes.
or as chord chart:
Move the chord to the 14th fret position, and you will get the E 6/9+ (Eastbound Train) or – one octave lower – to the 2nd fret (The Bug)
In Gravy Train this chord appears as A 6/9+, which is at the 7th fret posiotion.
Here is a sound clips with the ‘train excerpt’ from the mentioned songs:
Keep on whistling 🙂