Staff at Copleston high in Ipswich borrowed the museum pieces after an arson attack on the school put their electric bells out of action only days before the start of term.
Prefects were drafted in to crank the "very loud" sirens' handles to mark the start and end of lessons until the bell system was fixed.
The sirens were a useful real-life illustration for the pupils' history lessons, which include the Second World War, as well as reinforcing the Dunkirk spirit felt by both staff and students in following the fire, said head Laurie Robinson.
The school's main block, built in 1939, which housed the staffroom, offices, laboratories and classrooms, was destroyed by the blaze on August 27. Bells, telephones and the computer system were knocked out.
Suffolk fire service think arsonists dropped burning material through a roof-light into the staffroom. Repairs could cost between pound;500,000 and pound;1 million.
Mr Robinson said: "The Friday before the fire I was really buoyed up - this summer we've had our best-ever A-level, GCSE and key stage 3 results.
"When I went in on Sunday evening a section of school was six inches deep in filthy black mess and the bricks were still glowing with heat."
As staff and contractors worked to clear up before the 1,800 pupils began a staggered return last week, Richard Gallington, the caretaker suggested the sirens. He also works at a recreated air raid shelter.
First, Mr Robinson consulted the school's neighbours and the local authorities. "It was loud. We didn't want people to think Ipswich was being flooded.
"But everyone warmed to the idea. There was a definite feeling of Dunkirk spirit in the school," he said.
Kate Lacey, Copleston's director of corporate affairs, said a rota of prefects sounded the sirens.
She said: "The prefects were desperate to get hold of them. They're hand-cranked, so we've got some muscular prefects now. The pupils loved it."
The antique sirens have now been returned to the museum.
Mr Robinson said: "One of the things that has really impressed me over the past two weeks is that everyone's been going through three emotions. There was a great deal of upset and sadness over the fire, then a short period of anger.
"But once everyone worked through that, which happened fairly fast, it was a case of 'let's roll our sleeves up and sort this out'. There's really been a positive and upbeat atmosphere."
Copleston high is a community comprehensive which gained specialist sports status in 2001.