World War One Diary for Friday, September 21, 1917:
Ypres: British take 3,243 PaWs on September 20 and 21, repulse attacks on ‘Tower Hamlets’ ridge.
Baltic Provinces: Russian XXVIII Corps evacuates Dvina bridgehead at Jakobstadt, held since October 1915. German Eighth Army (700 casualties) takes it with 4,000 PoWs and 50 guns. Courland proclaims independence and requests German protection.
Ypres: Royal Flying Corps Nos 100 and 101 Squadrons continue night bombing of Menin and Roulers against arriving German troops, using parachute flares (repeated September 25-26 and 26-27).