[1] First conceived in 1940, the plane was built in response to the arrival of modified Junkers Ju 86P bombers flying reconnaissance missions,[2] which suggested the Luftwaffe might attempt to re-open the bombing of England from high altitude.

[3] The most obvious feature was the enormous high aspect ratio wing, with a span on the production aircraft of 70 feet (21 m).

The armament − four Hispano 20 mm cannon − was the same as the Whirlwind's, but the Welkin carried the guns in a tray in its belly, which facilitated loading.

The Welkin was seriously handicapped by compressibility problems caused by its long, high aspect-ratio wing which needed to be thick at the root (thickness-to-chord ratio of about 19%) for strength reasons.

[7] A two-seat radar-equipped night fighter version known as the Welkin NF.Mk.II for specification F.9/43 was developed but only one was eventually produced as the variant was not ordered into production.

[8][9] By the time the Welkin Mk.I was complete and in production, it was apparent that the Luftwaffe was no longer conducting high altitude missions, due largely to successful interceptions by specially modified Supermarine Spitfires.

[11] Data from British Aircraft of world War Two : Westland Welkin,[12] RAF Fighters, Part 3[13]General characteristics Performance Armament