Hello Brian,
check the position with this data for U-Boats on 01.-15.4.1940:
http://ktb.ubootwaffe.net/ktb041940a.zip
I didn´t check the positions, but:
14.46 Uhr U-2 (Planquadrat AN 26xx) muß vor einem britischen Flugzeug vom WELLINGTON-Typ tauchen.
There are some other attacks/actions by/with U-Boats/Escorts.
Greetings
Darius