U-boats in the Kiel Canal

[Cybermat47]

I was wondering, did U-boats actually use the Kiel canal when travelling from the Baltic to the North Sea? After all, the canal is rather shallow, meaning that diving wasn't an option in case aircraft attacked, and early on in the war formations of British bombers had been operating over nearby Heligoland, while the Skaggerak route provided waters deep enough to safely dive.