They make an important contribution to marine snow, since Oikopleura is abundant and is a very active filterer, using powerful strokes of its tail.

The Filterer's ability to correlate the information quickly and assess the probability of the true radar picture underpinned the successful operation of the whole radar system."

Much depended on the Filterer's detailed knowledge of the performance and limitations of each individual radar and their confidence in the ability of the crews on watch.

The Filterer's duty "was to decide the moment when a few successive plots, with all their possible inaccuracies, might be considered as a reliable track, fit for the operations room to act on for fighter interception".

She was later posted to 10 Group Fighter Command at RAF Rudloe Manor, near Bath, where she proved herself to be fast and accurate enough to be commissioned as a Filterer Officer.

Constantly on the horns of a dilemma, the Filterer had to decide "whether to put down an arrow on the strength of his (her) first guess, or to wait for another plot in the hope that it would confirm or confound his (her) suspicions."