any means of navigation including dead reckoning. When they were near the location, the transponder was activated and the Oboe station would measure their distance. This "cat" station would then send out a voice-frequency radio signal of either dots or dashes, allowing the pilot to adjust the path to be at the right distance, where the transmission would be a steady tone, the "equisignal". Operators would watch the position of the aircraft, sending out correcting signals as needed so the pilot could adjust the path along the arc. A second station would also measure the distance to the bomber. This station was equipped with the bomb's range value calculated earlier and had used this to calculate the distance between their station and the bomber at the point where the bombs should be dropped. When this mouse station saw the bomber approaching the drop point, it sent Morse code signals to inform the pilot that the drop point was approaching. At the right moment, it would send another morse signal that would drop the bombs automatically. The main constraint with Oboe was that it could only be used by one aircraft at a time. As it took about ten minutes for the bomber to get onto the arc, this delay meant that the system could not be used for a large raid with aircraft in succession. Instead, Oboe was used to guide the target marking aircraft of the pathfinder force, giving the main force of bombers an accurate aiming point in any weather. Oboe was sometimes used for attacks on point targets by one or a small number of aircraft dropping one after the other. In tests, Oboe demonstrated accuracies greater than those of optical bombsights during daylight in good weather. A new approach Oboe was limited to one aircraft because the onboard transponder would send pulses every time the ground stations queried them. If more than one aircraft turned on their transponder, the ground stations would start to receive several return pulses for every query, with no way to distinguish between them. One solution to this problem is to have each Oboe station send out a slightly different signal, normally by changing the envelope of the signal it broadcasts to the aircraft. Similar stations with different signal modifications can be situated around the UK, so that all of them are visible to an aircraft over Germany. An aircraft that turns