be used. An identical utilisation of the V-1 flying tank for the Ar 234 bomber was also investigated, with the same conclusions reached. Some of the "flying fuel tanks" used in trials utilised a cumbersome fixed and spatted undercarriage arrangement, which (along with being pointless) merely increased the drag and stability problems already inherent in the design. F-1 version One variant of the basic Fi 103 design did see operational use. The progressive loss of French launch sites as 1944 proceeded and the area of territory under German control shrank meant that soon the V-1 would lack the range to hit targets in England. Air launching was one alternative utilised, but the most obvious solution was to extend the missile's range. Thus the F-1 version developed. The weapon's fuel tank was increased in size, with a corresponding reduction in the capacity of the warhead. Additionally, the nose cones and wings of the F-1 models were made of wood, affording a considerable weight saving. With these modifications, the V-1 could be fired at London and nearby urban centres from prospective ground sites in the Netherlands. Frantic efforts were made to construct a sufficient number of F-1s in order to allow a large-scale bombardment campaign to coincide with the Ardennes Offensive, but numerous factors (bombing of the factories producing the missiles, shortages of steel and rail transport, the chaotic tactical situation Germany was facing at this point in the war, etc.) delayed the delivery of these long-range V-1s until February/March 1945. Beginning on 2 March 1945, slightly more than three weeks before the V-1 campaign finally ended, several hundred F-1s were launched at Britain from Dutch sites under Operation "Zeppelin". Frustrated by increasing Allied dominance in the air, Germany also employed V-1s to attack the RAF's forward airfields, such as Volkel, in the Netherlands. FZG-76 version There was also a turbojet-propelled upgraded variant proposed, meant to use the Porsche 109-005 low-cost turbojet engine with about thrust. Success of operations Almost 30,000 V-1s were made; by March 1944, they were each produced in 350 hours (including 120 for the autopilot), at a cost of just 4% of a V-2, which delivered a comparable payload. Approximately 10,000 were fired at England; 2,419 reached London, killing about 6,184 people and injuring 17,981. The greatest density of hits was received by Croydon, on the south-east fringe of London. Antwerp, Belgium was hit by 2,448 V-1s from