So there I was, on my 9th patrol in a TypeIIA in Feb '40. Set up a perfect 500m broadside of a lone cargo ship in relatively calm seas (winds were 4-6 kts). Fired at 0 gyro angle and watched the torp pass by, missing the target. Upset as missing the simple shot (torp went too deep), I turned my boat to fire another at its stern at 0 gyro...it too missed.
Now pissed, I surfaced and started strafing the ship with my 20mm Flak gun. Blew up the cargo, the bridge, and other stuff until the ship exploded and sank.
Later that night, I came across a lone motor vessel. Instead of wasting a torp (would be overkill and certainly a waste), I closed and peppered her with my Flak too. She went down easily.
There's something satasfying about killing something slowly with bullets, when you're pissed and want revenge.
