That formula, a classic celebration of the British amateur, reached its 30th anniversary yesterday, still pulling in millions of viewers for the BBC.
The surviving members of the cast, including Clive Dunn, Bill Pertwee and Ian Lavender, joined the sitcom's writers David Croft and Jimmy Perry for a reunion at the Imperial War Museum in London to mark the transmission of the first episode in July 1968.
Eighty episodes were made, telling of the war-time adventures of Capt Mainwaring and the motley crew of the Walmington-on-Sea Home Guard.
That first, black and white series is being re-shown on BBC 2 and attracting 4.6m viewers, making it the channel's third-highest show in the ratings. It is outperforming BBC 2 repeats of Have I Got News For You, and almost matching Channel 4's expensive import Friends.
When the series was shown on BBC 1 last year at a peak hour on Saturday nights it had an average of 7 million viewers and a 40 per cent share of viewing, beating more contemporary comedies, such as The Simpsons, in the same slot.
At its peak the figures were far higher. With its theme tune of "Who do you think you are kidding Mr Hitler" it drew 21 million viewers, more than soap heavyweights such as Coronation Street and EastEnders do today.
Geoffrey Perkins, the BBC's head of comedy, believes the show has been critically re-evaluated since its first run. "A lot of contemporary comedy writers had thought it slapstick, but watching it again they appreciate the characterisation and the writing.
"When it first appeared it was not thought likely to be a classic. It was regarded by one critic as full of gags, not characters, which is just nonsense. It was also regarded as controversial because it was still close to the war and it was thought to be disrespectful."
Graham Linehan, the co-creator of Father Ted, says creating a classic can be a matter of chance. "Hitting on a bunch of characters who work well together is almost entirely to do with luck. When Arthur Matthews and I started writing Father Ted we just wanted it to be funny, we didn't know you needed characters that work well together for it to be long-running."
Linehan believes Dad's Army was modern. "The first episode begins with them all made-up as even older, old men reminiscing about the war, so the whole thing is really one long flashback - almost as if they knew it would be a classic.
"It's genius. It is brilliantly weird having an army with an incontinent soldier and a corporal saying, 'Would you mind awfully falling in,' and them fighting about who gets to hold the gun. I love it."
The class warfare between Mainwaring and Wilson, once represented by a monocle, was a key element. When it was first being filmed BBC managers could never understand why the most upper-class officer, played by John Le Mesurier, was being ordered around by Arthur Lowe's middle-class bank manager.
"There are a lot of myths about how that got started," said Jimmy Perry yesterday. "But we decided it was funnier to have the grammar-school boy in charge of the public-school idiot. In fact they were both idiots, but in different ways. It is always funnier to have the idiots in charge. That's how Fawlty Towers works too."
Croft and Perry are not keen to analyse their comedy, but David Croft concedes they operated by rules. "It was well-intentioned, not harmful. Something happened, they didn't just sit on a sofa and talk, and although they were amateurs they would always win out in the end."
Kevin Lygo, Channel 4's head of entertainment, believes it is a classic because it is inclusive. "Old people and kids get something from it. Almost every classic comedy is non-exclusive. And as a nation we love the failing Brit. It's why we love Del Boy."