Angel of Mercy live in early 1979 – Mark Knopfler on slide guitar
Mark Knopfler never played that much bottle-neck guitar on his albums or concerts, nevertheless he occasionally did: except Water of Love from the first Dire Straits album of course, songs like The Man’s too strong (from Brothers in Arms), Do America (from Sailing to Philadelphia), Money for Nothing intro (live version 2001 tour), or Right now (All the roadrunning) come to mind. (I guess there are more, but before thinking about these for too long I will leave it to you to add these with the comment function below this article).
One song that was normally never played with a slide guitar is Angel of Mercy from Dire Straits’ Communiqué album (1979). However, the live version we have on some bootleg recordings from Germany, February 1979 features a slide lead guitar. On this tour Angel of Mercy was played as an encore, see more on this in this forum thread.

Before many will ask where they can hear this recording, I thought to write this article to include an audio clip. Enjoy:
Dire Straits, Angel of Mercy, Mannheim, Germany, February 14, 1979
Edit March 27: original text:
By the way, I have no idea which guitar he is playing here. Normally they had a black Fender Telecaster Thinline (from around 1969) tuned to open A on which Mark played Water of Love. So it would make sense that it is also the black Tele, as the Strats were setup for normal playing with an action probably not suited for bottle-neck. On the other hand, Angel of Mercy does not call for an open tuning. I am afraid we will probably never know for sure 🙁
Update March 27:
If you read the comments to this article, you have probably seen the following picturs (thanks to Brunno):

The description at Getty Images says that it was taken in Rotterdam, October 19, 1978 (like four other pictures , see also this article), but I think this picture one (and one other) are in fact from early 1979 (similar but not identical clothes, different guitar, Mark is wearing a neck lace, etc.). If so, this picture is the proof for a 12-string (a Burns Baldwin Double Six by the way) played with bottle-neck, and the song can be no other than Angel of Mercy.
















The Imperial is a two-channel combo with reverb and tremolo. The output power is about 20 watts, coming from two 6V6 tubes. The two channel make use of 12AX7 pre-amp tube, and one 12AT7 driving the reverb, just like Fender amps from the sixties or seventies. In fact it reminds me a lot of a black-face Fender Deluxe amp, which also has a similar layout and one 12″ speaker. In fact you can read on the Tone King website that the rhythm channel aims for that Fender black-face sound. A volume, treble and bass control is all that is required here. Of course the spring reverb – a fundamental ingredient of the Fender sound – works for both channels (note that on Fender amps it only affects the second channel). It will not surprise you that the reverb circuit uses the same two-spring reverb tank (acutronics) and the same tubes like Fender.
The second channel also features just three controls: volume, tone and mid-bite – so no bass and treble control here, just on a small Fender tweed amp from the 50ies. The mid-bite adds a midrange peak and tightens the low end, controling the overdrive tone character that can be blended from Fender tweed to Marshall style.


