The General Electric B-3 was a standard turbo-supercharger used in various US WW2 aircraft including the B-17, B-24, and P-38.
This cut-away model shows the the operating principle to advantage. Hot engine exhaust entering at right is directed upwards through a single-stage turbine visible on top.
The turbine is on a common shaft with the single-stage centrifugal compressor at the bottom. Pressure is regulated by the 'waste-gate' valve at upper left.
A ram-air scoop on top and a flow path around the shaft housing provide air cooling to the turbine disc.