http://www.navweaps.com/Weapons/WAMBR_ASW.htm
http://www.navweaps.com/Weapons/WAMUS_ASW.htm
What was "always" true got a lot of u-boat crews killed.
By 1940 British depth charges were being set as deep as 300 feet. Of course a u-boat could dive deeper than that.
Note that the British Mk X* came out in 1943 and could be set as deep as 640 feet.
What was true in 1939 was no longer true in 1943. Diving deep did not help against a British Mk X* or Mk X**, or against an American Mark 8; especially not against hedgehogs.