Johnson boiler

[2] This was a time when water-tube boilers were being adopted in fast turbine ships, such as naval warships and passenger liners.

[4] The large radiant heating area available allows a combustion rate, for a given furnace volume, of around twice that for a contemporary boiler, such as the Yarrow.

The small amount of brickwork for the Johnson design, without requiring a furnace base, was seen as an advantage by the Navy.

The initial design had poor circulation until external cold downcomers were added, increasing the weight by 10%.

[7] The superheater would be placed in one side of the uptake, with a reheater between the high and low pressure turbines placed in the other.