Would this be the book that had a line of airmen on a fod plod after an aircraft crash and one of them kicked what he thought was a leather football to find it was a flying helmet complete with head?
... exactly so
xenolith - well nearly so.
IIRC "our hero" on the fod-plod had been instructed NOT to pick up or touch anything but just report it. Chummy sees leather flying helmet, thinks he'll nick it, so picks it up and .......
But it was a long time ago I read it - at Guetersloh* strangely enough ....
*[pedant protection measure - I'm not clever enough to do a u-umlaut, so it is conventional to insert an "e" after the umlauted vowel]