for this battle had not however reached the Jagdstaffeln in sufficient numbers, despite its own premier on the Western Front in the mid-Spring of 1918. As with several offensives on both sides, thorough planning and preparation led to initial success, and in fact to deeper penetration than had been achieved by either side since 1914. Many British airfields had to be abandoned to the advancing Germans in a new war of movement. Losses of aircraft and their crew were very heavy on both sides – especially to light anti-aircraft fire. However, by the time of the death of Manfred von Richthofen, the famed Red Baron, on 21 April, the great offensive had largely stalled. The new German fighters had still not arrived, and the British still held general air superiority. The month of April 1918 began with the consolidation of the separate British RFC and RNAS air services into the Royal Air Force, the first independent air arm not subordinate to its national army or navy. By the end of April, the new Fokker, Pfalz and Roland fighters had finally begun to replace the obsolescent equipment of the Jagdstaffeln, but this did not proceed with as much dispatch as it might have, due to increasing shortages of supplies on the side of the Central Powers, and many of the Jastas still flew Albatros D types at the time of the armistice. The rotary engined Fokker D.VIII and Siemens-Schuckert D.IV, as well as surviving Fokker Triplanes, suffered from poor reliability and shortened engine life due to the Voltol-based oil that was used to replace scarce castor oil – captured and salvaged Allied aircraft (especially Sopwith Camels) were scrounged, not only for engines and equipment, but even for their lubricants. Nonetheless, by September, casualties in the RFC had reached the highest level since "Bloody April" – and the Allies were maintaining air superiority by weight of numbers rather than technical superiority. Readying for battle 1918, especially the second half of the year, also saw the United States increasingly involved with the allied aerial efforts. While American volunteers had been flying in Allied squadrons since the early years of the war, not until 1918 did all-American squadrons begin active operations. Technically America had fallen well behind the European powers in aviation, and no American designed types saw action, with the exception of the Curtiss flying boats. At first, the Americans were supplied with