LONDON — Harried commuters here have heard it all. Delays due to nasty weather, terrorist attacks, endless repairs. But here's a fresh one: All flights to and from London City Airport were canceled Monday after an unexploded World War II bomb was found buried in the muck of the River Thames near the end of a runway.

The local Evening Standard reported: “The airport will remain shut throughout Monday, affecting up to 16,000 passengers.”

Scotland Yard said, essentially, that it is a very big, very old bomb — a tapered-end shell about five feet long that weighs half a ton. Think the heft of a grand piano.

There is no word yet from the navy divers on whose bomb it was — although a good guess as to the owner might be the German Luftwaffe, which waged the Blitz in 1940 and 1941, the eight-month aerial bombardment of military and civilian targets in Britain during World War II. London alone endured 57 consecutive nights of bombing. About 43,000 people died, and 1 million were left homeless.

According to an article in the Express newspaper about the Blitz, “Fears of bombing led to 750,000 domestic pets being put down. London Zoo destroyed all its poisonous snakes and spiders.”

In total, about 50,000 tons of high-explosive bombs were dropped during the Blitz. Wide swaths of the city were destroyed by the bombs and resulting fires.

But half the shells were duds.

A spokesman for London police said Monday that construction crews discovered this particular bomb buried under 30 feet of ooze in the Thames at the King George V Dock near one end of London City Airport. The dock area was a frequent target of German bombing during the war.

“It is lying in a bed of dense silt and the first stage of the removal operation is to free the shell from the silt so that it can be floated for removal,” Scotland Yard said in a statement.

“The operation to remove the ordnance is ongoing in partnership with our colleagues in the Royal Navy. The timing of removal is dependent on the tides, however, at this stage we estimate that the removal of the device from location will be completed by tomorrow morning,” the statement said.

Emergency crews set up a security zone of about 300 yards around the bomb for most of the day Monday. They later allowed local residents to return to their homes and shops.

The Royal Navy said it would tow the bomb by inflatable craft down the Thames and explode the ordnance, underwater, in an empty stretch of the river.

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