Lt Cdr Ben Brown, commanding officer of the Royal Navy's Bravo Squadron bomb disposal team, said the bomb is "on the larger side" of what they usually deal with. He explained: "It's 250lbs, an American general purpose bomb of the World War Two era."
He added: "This could have come from any number of sources. It could have been an American bomber that's come back from a mission, not successfully executed that, not dropped its payload and it needed to get rid of the bombs before it landed. It could have been an emergency and it needed to just ditch."
He told BBC Radio Cornwall each scenario was different when ordnance was found. "You could put the same bomb in a slightly different location, on a different day, with different weather conditions, and have a completely different response required," he said.
He also said: "This is on the larger side of ordnance that we would deal with, but the Plymouth team in particular have dealt with a lot of these recently, certainly this year to date, but it's on the slightly larger side."
Falmouth WW2 Bomb Prompts Evacuation of 300 Homes