Builders who started drilling the walls of empty flats were shocked when live Second World War ammunition fell through the plaster.
They were working on flats above the former Kazbah pub on Marine Parade, and were astonished when 20 bullets, some dated 1942 and 1944, fell out.
As they peered into the hole, they also found two empty envelopes of French-Canadian standard issue ammo, dated 1944 and addressed to a Miss Rollande Bellaoonce in Canada.
Foreman Ben Webb said: "We were doing a routine inspection, putting holes in the walls to find out what was behind them.
"We pulled a part of it down and the bullets fell out. It's like nothing I have ever come across before. I don't know how they would have got there.
"I was shocked when the bullets fell out and scattered across the floor. Work halted immediately."
Police removed the ammunition and the envelopes could go to Worthing Museum.
Hundreds of French-Canadian soldiers were stationed in Worthing during the war and many took part in the ill-fated 1942 raid on Dieppe.
They were billeted in properties overlooking the seafront after civilians were evacuated.
The flats above the Kazbah have an uninterrupted view of the pier and may have been used as an observation post or machine gun nest.
They are being renovated after a fire in October.
Worthing had a love-hate wartime relationship with the French-Canadians, who had a reputation for toughness and drink-fuelled violence.
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