The Hillson FH 41 Firestorm
The Firestorm is one of the iconic ground attack aircraft of WW2, with its signature spinning incendiary dispenser featuring prominently in many war movies up to the present day. But its heyday over the mountains of Yugoslavia was incredibly brief, and its far more famous use in Normandy was effectively little more than a dramatic morale-booster for the allied soldiers on the ground. Nonetheless, the fascinating history of this aircraft is well worth a closer examination than it is often given...
When Noel Pemberton Billing, founder of the Supermarine Corporation, publicly accused Lady Asquith, wife of the then Prime Minister, of being a lesbian (and possible blackmailed German spy)[1] his days as head of a major firm reliant on government orders were numbered. Even the fall of Asquith's government did nothing to retrieve his reputation in the circles where aircraft purchasing decisions were made. This led to his erratic post-first-world-war career, primarily running a series of mostly unsuccessful publications supporting aeronautics and right-wing politics. His connections to Oswald Mosley came at just the right moment to get him the funding he needed to create a new aviation firm, with investors attracted both to his strong right-wing political views and his bold proposals for revolutionary new aircraft[2]. Chief among his plans was the slip wing, a drop tank that would also provide lift when mounted above an airplane, which Billings believed would allow his aircraft to combine the strengths of both biplanes and monoplanes.
The outbreak of the Second World War and Billings' Nazi ties ended the new Billing's Aviation corporation, but the wind tunnel and flight testing data for the slip wing was taken over by F. Hills and Sons, a small engineering firm with ambitions in the aviation business, who were able to use the collected data to relatively quickly and easily develop the Hillson FH 40, a Hawker Hurricane adapted to carry a slip wing. The FH 40 was produced in low volumes, but the high cost of the slip wings and their low recovery rate kept it from being a truly successful project. The only notable contribution made to the war effort was the delivery of several squadrons of FH 40s to Malta by air from Gibraltar, taking advantage of the extended range the slip wing drop tank concept offered for the ferry flight but otherwise operating as normal Hurricanes.
It would be the survivors amongst these airframes that would provide the genesis for the FH 41 program. By 1943 the Hurricane was no longer an effective front-line fighter, but the Mediterranean theater was always too pressed for new aircraft to discard perfectly operable airframes. Instead, the surviving FH 40s were sent to join the Balkans Air Force, operated by a scratch squadron of Italian pilots and used as a ground attack aircraft flying from the island of Vis and operating in support of the Yugoslav partisans. It was apparently one of the Italian pilots, or perhaps the squadron's ground crew, who had the bright idea of modifying the remaining stocks of slip wings to serve as rudimentary bombs as an unconventional way of increasing the Hurricane's bombload.
Word of this found its way back to Hill and Sons, who were apparently inspired to develop a purpose-built version of the concept. The result was a slip wing deliberately designed to be rotationally unstable, so that once released in flight it would begin to spin. This was then loaded with incendiary submunitions. The concept was that the slip wing would be released at high speeds but low altitudes, and scatter incendiaries across a wide area as a way of destroying soft targets, particularly artillery. Several prototypes were hurriedly developed and dispatched to Vis, where they proved spectacular, but were judged overly expensive for the results achieved. Nonetheless, they are reported to have had some morale effects upon the second-line German troops assigned to garrison duty in the Balkans theater.
The final remaining FH 41 slip wings were expended over the Normandy battlefields in the early portion of the campaign, earning much press attention and praise from the allied infantry who liked seeing such obvious signs of air support. However, by this time the Hurricanes carrying the Firestorms were clearly obsolete, and proposals to modify more modern fighters to carry them were summarily rejected by both the RAF and the USAAF.
Scenes in movies such as The Battle of Britain (where a German flying officer goes from mocking the British for sending up biplanes to obvious terror when an entire squadron of FH 40s drop their slip wings in unison) or Saving Private Ryan (where a single FH 41 drop eliminates a battery of closely-packed German anti-tank guns) have unfortunately misled generations of viewers into believing that the Hillson's aircraft were more common than they were, but the FH 41 Firestorm is nonetheless a fascinating example of the ingenuity of armaments designers of the Second World War.
[1]This is all OTL; Maud Allen was also named in the same article and sued Billings for defamation, so much information on the case is readily available for the curious among you.
[2]Billings choosing not to emigrate to Australia and eventually raising enough money to try to actually pursue his ideas during the late 30s is the PoD of this concept. Billings was a big promoter of the slip wing concept in his various publications, and his extreme right-wing political contacts are well-documented.