Possible Clues:

• Eavesdrop
• Accidentally perceive with the ear
• Accidentally listen to
• Listen accidentally without speaker's knowledge
• Catch what was said of Americans in Britain
• Eavesdrop on
• Catch report of GIs in Britain during the war, as the saying goes
• Accidentally catch something, perhaps
• Pick up report of GIs' wartime location
• Is this what the earwig said about the GIs, reportedly, once in Britain?