The B-221 Scythe was an six-engine, mid-range, transatmospheric bomber, first used by the United Nations Space Command Navy during the Human-Covenant War. The Scythe's development began in late 2525 as it became readily apparent that existing spacecraft were wholly inadequate for combat against the Covenant, particularly in space, where the already in-demand F/A-352A Longsword strike fighter was pressed into service as a spatial bomber. The Scythe's development made use of various bleeding-edge technologies which had been developed in response to the existential threat posed by war with the Covenant. The result was that, when it entered service in 2537, the B-221 was the most expensive starfighter per airframe ever constructed.