DaveTurner

I don’t think a Clan was comparable with a Bulleid light Pacific. Putting aside the debate about the original design, the-rebuilds routinely did the work of Merchant Navy class 8s. Indeed at the 1948 exchanges the light pacifics showed exceptional power output though burnt more coal doing their work. The Britannia’s were probably equivalent to a Bulleid but the two cylinder arrangement was not so smooth at speed. Pacifics generally are less sure footed than 4-6-0s because the trailing truck can unload the the driving wheels especially on uneven track.

Essentially the signals were designed to control the movements required at a location. The golden rule is no train must pass a stop signal - so the position must protect whatever may be happening beyond this signal such as a conflicting movement. Where space permits at a junction the signal would be placed several yards ahead of the points so that if the signal is passed there is some leeway before a possible accident. As well as reading the books suggested it is worth visiting a heritage railway and looking at all the signals and working out what each does and why it is where it is. Watching as trains arrive and are shunted and which signals control each move really helps to understand it all. A friendly signalman may give you a tour of the box. One extra thing to look for is the main signals, calling on signals and shunting signals. Colour lights were in that era equivalent to semaphores.