Mosquitoes would be equipped with Oboe. Having faced opposition before, the addition of Oboe upset the argument against the specialist role, and what would become Pathfinder Force began forming over the ongoing objections. Into service The first experiments with Oboe in a combat setting over Germany began on the night of 20/21 December 1942, when a small force of six Oboe-equipped Mosquitoes were sent to bomb a power station at Lutterade in the Netherlands, on the German border. Three of the sets failed, but the three remaining aircraft, led by Squadron Leader L.E. Bufton, were able to drop properly. A follow-up reconnaissance mission the next day showed that nine of the bomb craters could be identified, all of them clustered closely together but some away from the target. Similar tests with small numbers of Oboe aircraft, sometimes dropping flares for small numbers of Avro Lancasters following them, were made throughout December and January. At first, the Germans wrote off these small attacks as nuisance raids, intended to upset production by sending the workers to the air raid shelters. However, it was soon realized that something very odd was occurring; aircraft were dropping only 6 to 10 bombs, often through heavy cloud cover, and having 80 to 90% of them hit their targets, normally blast furnaces or power stations. As part of this process, the bombers released photoflash flares, which lit up the ground below the aircraft enough for photography. On 7 January 1943, Hauptmann Alexander Dahl noted these and suggested that they were using the photographs to correct for measurement errors of a new bombing system. This was precisely what had been happening. Over the UK Oboe demonstrated accuracy on the order of tens of metres, but over the Continent the early tests always produced worse results. But it was soon clear there was a pattern to the misses, which was surmised to be due to differences in the surveying grids used on the continent. The solution to this problem was provided by the Germans themselves; before the war they had made an effort to calibrate the two systems in a series of cross-Channel measurements that the UK Ordnance Survey also received. Using these corrections they were able to address the inaccuracies almost immediately. By the late spring Bomber Command crews had practised the bomb-on-marker technique enough to begin major operations. Harris then began a series of raids known as