Thermocyclic heater.
This unit is mounted below the floor of the nearside crew seat and contains manual controls for the operation of the unit. A cover, secured by a single large handnut protects the controls from damage.
The heater is used to maintain engine coolant temperature above freezing and to provide additional heating, via a heat exchanger and fan,for the crew compartment, hose stowage's and the rear equipment stowage.