USSR has about 15,000 Polish officers held in 3 POW camps in western Belarus & Ukraine. Stalin & the Politburo decide to murder the officers & other Polish prisoners, fearing anti-Soviet resistance if they are released and declaring them “enemies of the Soviet Union”. The Polish officers at Kozelsk camp are shot & buried in a forest near the village of Katyn. The whole episode becomes known as Katyn massacre. http://en.wikipedia.org/wiki/File:Katyn_-_decision_of_massacre_p1.jpg
Finland. Red Army controls Viipuri Bay despite taking heavy losses from strafing by Finnish aircraft and shelling. They capture more islands and push inland on the Western shore. Clearly with the upper hand, USSR renews its peace offer on the same harsh terms that expired March 1. Finnish Government accepts defeat, its defenses crumbing, and decides to open peace talks.
At 9 PM, U-17 torpedoes Dutch steamer SS Grutto 20 miles from the Belgian coast. Grutto sinks in 6 minutes (all 18 hands lost). http://www.uboat.net/allies/merchants/ships/285.html