April 21, 1916
Air War:
Irish RFC pilot David Tidmarsh barely escapes death when an anti-aircraft shell passes through the cockpit of his DH.2.
Celtic Sea:
Raimund Weisbach, commanding
U-19, begins his career with the sinking of British freighter SS
Feliciana, 4,282 tons, travelling in ballast from Cardiff to New York.
German freighter SS
Libau, 1,062 tons, disguised as Norwegian SS
Aud departed Lübeck on April 9, with an all-volunteer crew heading for southern Ireland with a load of 20,000 rifles, one million rounds of ammunition, machine guns and explosives, all hidden under a load of timber. Managing to evade the British blockade and a major storm she arrived at Tralee bay on April 20th. The plan was to meet with traitor/spy Roger Casement. The plan failed and
Libau attempted to escape, but was captured by the blockade. On April 21st she was being escorted by sloop HMS
Bluebell when captain Karl Spindler and his crew scuttled their ship and were taken POW.
https://en.wikipedia.org/wiki/SS_Libau
North Sea:
French naval trawler
Estafette, 276 tons, hits a mine laid by Matthias von Schmettow in
UC-6, bringing his score to 35 ships and 47,333 tons.