Sentence:  Each airfield had its own <WSD>buncher</WSD> which emitted a particular radio signal. Each plane had a radio compass so that when we flew toward the <WSD>buncher</WSD>, the compass would go straight up. When we flew over the <WSD>buncher</WSD>, it would point straight down. 
Meaning of the word marked with <WSD> tags:  A ground-based radio transmitter, configured within a system to guide aircraft to their allocated airfields.