[Nick Beale]

From Bletchley Park's Air Operations Watch summary for 28/29 July (National Archives HW13/39):

"British sources report a ship in OMAHA anchorage attacked and sunk by bomb at 0125/29. Nothing available yet to tie up with this."

If that's your vessel and it was a bomb then KG 77 seem less likely as they were equipped for torpedoes at the time.

P.S. times in the report are "M.S.T." which I think is GMT+2.