> Also wondering: what replaced this!
A collection of smaller pumps and monitors, which is likely a better scheme, in terms of flexibility and fault tolerance. While a remarkable design, the single pump with long hoses to multiple hydrants, then radiating to multiple monitors, is a system that takes great coordination and precious time to deploy and rework in action.
The Napier Deltic engine is the party piece in all this. It is an ambitious and yet successful design, intended to push the limit of power-to-weight in a diesel engine. I investigated the state of current diesel locomotive engines in comparison to the Deltic and it remains, to this day, the highest power-to-weight diesel engine in use for locomotives. (There are half a dozen still running in the UK today in limited service.) I've personally visited the Bay City museum to see this engine.
These engines require forced induction; they cannot run naturally aspirated. In its various naval, rail and other applications there were many different induction designs applied to the Deltic: turbos, superchargers and combinations of both. Today, we have electric forced induction, enabled by the high performance electric motors that have emerged elsewhere in transport applications. One thinks of what diesel wonders might be created by combining the Deltic design with electric forced induction.