Why fly at armed U-boat in an unarmed plane?

Comment: Spotter planes tend to be lighter unarmed aircraft where extra fuel and weight savings are added and made allowing for extended idle or observation times on mission. In the absence of anything else before the patrol boat shows up they are probably doing a bit of intimidation. Not so much the submarine but more the rubber dingys trying to reach the submarine, perhaps break the pace of the germans and slow them down. The aircraft was actually a Percival Proctor 1, usually used for training flights when in service. This privately owned example, crashed in France 14 years later.