AFAI remember from my one visit to RPM is that the pic is taken from the north side and one can see the south part, so the harbour is on the left of the pic. And the high walls are still there

Compare this image with this one that was taken on the same spot nearly half a century later. Mechanised coal conveyor to manual refuelling in fifty years - what a progress!

All the pictures here are of Madras and Southern Mahratta Railway (MSMR). The boat Mail was operated by South Indian Railway (SIR).

This is an XB class locomotive since MSMR did not have any locomotives of the XC class. Many of the MSMR express locomotives including this one were christened as can be seen from the name plate of this locomotive above the middle driving wheel.

My guess is that this loco has overshot the semaphore signal at danger and come to grief in the de-railment dead end pit.

Yes. This, indeed, is S. It has a sharp curved platform with Cavery river bridge on both sides - S is an island with the river Cavery splitting into two branches and the joining again as one at a point called "Sangama".

It is a real challenge to build the second BG line (doubling) with a sharper curve.

This is a BG loco. The Boat Mail in that era must have been MG.

Is this today's Shrirangapattana (with a rare single letter station code - 'S')?

Why did Royapuram platform have such high walls? Do these walls survive even today? How is this view shot (which is the high vantage point in the area) and which side the harbour?

This is the Boat Mail accident of 1928. I dont remember the exact date. There is a chapter on this accident in the book "Southern Railways, 150 Glorious years" by Sri. R.R Bhandari