Fairey P-24 Monarch, (1939), 2,240 hp, a more powerful development of the Prince H-16 with greater capacity. 24-cylinder 'double' engine, in-line vertically opposed monobloc castings, H-shaped, poppet valve, liquid cooled. Bore/stroke 5.25 x 6.0 in (133.35 x 152.4 mm), vol. 3,117 cu in, 51.08 litre. Compression ratio 6:1. Four speed, two stage supercharged. Geared, spur .543:1. Independently controlled and synchronised, co-axial counter rotating and feathering LH (front), RH (rear) propeller drives. Length 86.25 in; width 43.0 in height 52.5 in. Aircraft Fairey Battle I
Fairey V-12 Prince I, 650/670 hp and Super Prince II, 720 hp, 12 cylinder upright 60 degree Vee shaped, poppet valve, water cooled engine. It was built in two versions, unsupercharged and fully supercharged, but exact details are few. Its propeller drive was spur geared, RH tractor drive. Bore/stroke 5.25 x 6.0 in Vol 1,558.62 cu in, 25.54 litre. The fully supercharged version designated V-12S, Prince II (or probably Super Prince was intended to develop 720 hp at 2,500 rpm at 12,000 ft for a modest dry weight of 1,150 lb. Aircraft: Fairey Fox II (probably the Prince I but uncertain.)
The first real Fairey engine was designed in considerable secrecy. It was intended to be directly competitive with RR's highly supercharged P.V.12 (later named Merlin). It was designated the Fairey P.12 and given the name Prince. This was built and run in two versions, labelled according to the degree of supercharging... By the end of 1934, three engines had completed 550 hours of bench running, including ten hours at 420 hp and three hours at 700 hp. One Prince was flown in Belgian Fairey Fox II.
As Shortround says, it is unlikely that the P.24 had a 4 speed two stage supercharger. As it was basically two engines on a single crankcase it is most likely that each half had a single stage two speed supercharger.
I did at one stage have a USAAF report on the P.24, which evidently didn't like some of the features of the engine - like the cranks not having counterweights.
look at the raised horizontal castings going from the centre to the exhaust ports; these look like they could contain the rocker push rods.