World War One Diary for Thursday, July 12, 1917:

Western Front

Flanders – FIRST USE OF MUSTARD GAS: Germans fire 50,000 rounds (125t) at British near Ypres (Allies dub it Yperite), 2,490 gassed (87 deaths), mainly in 15th Division.

Sea War

North Sea: Destroyer HMS Patriot depth charges and sinks U-69 east of Shetlands.

Air War

Western Front: Mannock scores 4 victories (until July 13). Record air activity to date including 30 Anglo­-French fighters vs 30 German (2 lost) on day that costs 9 British and 14 German aircraft.

Palestine: Allenby asks for 3 more Royal Flying Corps Squadrons, gets 2 by September.