25-31 January 1943


12 Sqn suffered no casualties during this week but did dispatch 13 aircraft on missions to Dusseldorf and Hamburg, although only 6 attacked the targets. Bad weather was the order of the day for most of the week.

This week also saw the first use of “ground marking” using Oboe by Pathfinder Mosquitoes in the attack on Dusseldorf and the first H2S attack of the war, with Pathfinder Stirlings and Halifaxes using the device to mark targets in Hamburg.

Oboe was a British bomb aiming system developed to allow their aircraft to bomb targets accurately in any type of weather, day or night. Oboe coupled radar tracking with radio transponder technology. The guidance system used two well separated radar stations to track the aircraft. Each Oboe tracking station used radio ranging to define a circle, the radius of which was the distance from the station to the target, the third point in the triangulation. The two circles intersected at the target. Radar pulses from each station were picked up by a transponder mounted in the aircraft. The aircraft transponder transmitted the signals back to the stations, after a slight delay. By assessing the time it took for the signal to return the distance between the station and the aircraft could be determined. One tracking station, the Cat station, was used to adjust the aircraft’s flight path. The other station, the Mouse, was used to key the bomb release point. Oboe, in essence, was a ground-controlled, blind bombing system. (Wikipedia)

An illustration of Oboe. Two radar stations track the flight of the aircraft. The southern station is the Cat which generates pulses whose arc is defined by the distance from the station to the target. The aircraft will fly along the arc from a start point ten minutes flight from the target. As it approaches the intersect with the arc from the Mouse station the aircraft is signaled to prepare for bomb release. When the aircraft reaches the point where the two arcs intersect the Mouse station transmits the signal to release bombs. (Wikipedia)

H2S was the first airborneground scanning radar system. It was developed to identify targets on the ground for night and all-weather bombing. This allowed attacks outside the range of the various radio navigation aids like Gee or Oboe, which were limited to about 350 kilometres (220 mi). It was also widely used as a general navigation system, allowing landmarks to be identified at long range. (Wikipedia)

A photograph of the H2S display taken during an attack on Cologne – the annotations were added later for post attack analysis. The river Rhine is visible snaking from top to lower right. (Wikipedia)

Extract from 12 Sqn Diary

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