The Napier Dagger was FB Halford’s most successful air-cooled engine design for Napier. The 24-cylinder supercharged engine was of vertical ‘H’ configuration with twin crankshafts geared together. It included Halford patented hudraulic tappets operated from its four sets of single overhead camshaft gear
Flight testing was carried out by Fairey’s test pilot, Chris Staniland, in a Fairey battle. Despite receiving the full support of the Air Ministry this engine failed to break into the market in a big way. The engines were fitted in the Hawker Hector and the twin engined Handley Page Hereford light bomber which saw active service in Europe and North Atlantic early in WWII.