Possible Clues:

• Thick fog
• Dense, dirty fog
• Dense fog
• Thick smokey fog
• Spooner's glimpse behind Spooner's obscuration?
• Initial course taken by soldiers returning in thick fog
• Training twice, latterly in a bad-tempered haze
• Thick yellow fog of old
• In London, particular coin wonderful to hear of
• Foggy conditions pose a problem — pure chaos