Then in early March 1944, British Intelligence Headquarters received a report of a Polish Underground worker (code name "Makary") who had crawled up to the Blizna railway line and saw on a flatcar heavily guarded by SS troops "an object which, though covered by a tarpaulin, bore every resemblance to a monstrous torpedo." The Polish intelligence also informed the British about usage of liquid oxygen in a radio report from June 12, 1944. Some experts within both British and Polish intelligence communities quickly realized that learning the nature of the fuel utilized by the rockets was crucial, and hence, the need to obtain a working example.