Fifty years ago, on March 3, 1965, Rogers and Hammerstein’s blockbuster musical The Sound of Music was released in American cinemas.

While the film has gone on to be one of the most beloved movies in history, at the time of its release it was a critical flop.

That didn’t stop millions of filmgoers latching onto the classic for the rest of their lives.

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Whether it was the romance between Maria (Julie Andrews) and Captain von Trapp (Christopher Plummer), the music, the children, the nuns or the Nazi escape plot, everyone loves this film for their own reasons.

On its 50th anniversary, here are 10 essential Sound of Music film facts:

1. It was a critical flop

It may be one of the most iconic films in cinema history, but when The Sound of Music premiered in March 1965, top film critics savaged the movie.

The New Yorker’s famed pundit Pauline Kael said it was “the single most repressive influence on artistic freedom in movies”.

She wasn’t alone in her disdain of the film, with The New York Times critic Bosley Crowther calling it “cosy cum corny”, among many other nasty reviews.

Director Robert Wise took it in his stride: “The East Coast, intellectual papers and magazines destroyed us, but the local papers and trades gave us great reviews.”

2. Christopher Plummer turned down the role of the Captain

Christopher Plummer wasn’t the first choice to play Captain von Trapp and he didn’t want the role to begin with, calling it “The Sound of Mucus”.

Initially, director Wise – who was also dubious about the movie, turning it down three times – looked at casting Sean Connery and Richard Burton.

Plummer told an awards season roundtable in 2012 that it was the hardest role of his career.

“Because it was so awful and sentimental and gooey,” he explained. “You had to work terribly hard to try and infuse some miniscule bit of humour into it.”

He’s recently changed his tune, telling Vanity Fair this month: “As cynical as I always was about The Sound of Music, I do respect that it is a bit of relief from all the gunfire and car chases you see these days.

“It’s sort of wonderfully, old-fashionedly universal. It’s got the bad guys and the Alps; it’s got Julie and sentiment in bucketloads.”

3. The opening scene was a safety hazard

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The most iconic film opening in cinema history, Wise used a helicopter to capture Andrews singing ‘The Sound of Music’ atop the Bavarian Alps.

While the helicopter shoot was eventually a success, with the sweeping cinematic footage of Andrews and The Alps captivating, the filming was hazardous.

Every time the aircraft came close to the actress for a close up she was floored.

4. Charmain Carr (Liesl) had a huge crush on Plummer

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She may have played his 16-year-old daughter Liesl, in love with the Nazi soldier Rolfe, but in reality 21-year-old Charmain Carr only had eyes for Plummer.

“I had a huge crush on him,” Carr told Oprah Winfrey in 2010.

“He was so perfect, and he spoke with this perfect British accent.”

He also got her drunk for the first time.

Any fan of the film can clearly see her googly eyes as they sing ‘Edelweiss’ together and Plummer has admitted the feeling was mutual – although it never developed.

5. Peggy Wood did not sing ‘Climb Every Mountain’

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‘Climb Every Mountain’ is the great crescendo of the film and theatre star Peggy Wood played the Mother Abbess who convinced Maria to return to the von Trapp’s from the abbey.

Wood was a well-known singer in her own right but at age 72 she considered herself too old to sing the part required and was dubbed.

The New York actress also had trouble lip-synching, hence why she is gazing out the window, giving the scene a more dramatic effect.

6. The children are still great friends

From left: Kym Karath (Gretl), Debbie Turner (Marta), Angela Cartwright (Brigitta), Duane Chase (Kurt), Heather Menzies (Louisa), Nicholas Hammond (Freidrich), and Charmian Carr (Leisl). Photo: Vanity Fair

It may have been 50 years since they won their starring roles in the film, but the Sound of Music Seven – as they call themselves – are still good friends.

Despite none of the children going on to majorly successful acting careers, they have happily lived in the shadow of the movie.

Here’s a pic at the premiere 50 years ago . The VF FB pic is at 7000+ ! @DebbieTurner_ @nicholasham1 @VanityFair pic.twitter.com/C5ls9MZxZO

— Kym Karath (@KymKarath) March 2, 2015

One nice tidbit: Nicholas Hammond, who played the oldest son, Freidrich, has lived in Australia since the mid-1980s and is the partner of acclaimed Australian theatre actor and director Robyn Nevin.

The leads, Plummer and Andrews, have also remained close friends since making the film.

7. The wedding did not have a priest

Apparently someone forgot to wake the actor who was playing the part of the priest officiating the wedding between Maria and the Captain.

It’s never hurt the film though, with thousands of people making the pilgrimage to Austria’s Mondsee Cathedral where the couple wed in the film, many to recreate Maria’s famous walk up the aisle.

8. Famous ghost singer Marni Nixon made a cameo

Marni Nixon (centre,) singing ‘Maria’ in her only film appearance.

Andrews was famously turned down for the lead role in My Fair Lady, which she had starred in on Broadway and the West End, instead being replaced by screen star Audrey Hepburn.

The only problem for Hepburn, she could’t sing and had to be dubbed by acclaimed ghost singer Marni Nixon, who had also sung for Natalie Wood in West Side Story and Deborah Kerr in The King and I.

In The Sound of Music, Nixon played Sister Sophia, one of the singing nuns – her only film role. Apparently Andrews professed to being a huge fan of her work.

9. The final scene filmed almost didn’t happen

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Wise chose the love scene between Maria and the Captain as the last to be filmed of the 11-week shoot.

Unfortunately, the lights being used were constantly blowing “rasberries”, making it impossible for Andrews and Plummer to keep straight faces while they were meant to be professing their mutual love.

When you watch the film, they are filmed in sillouhette as they sing ‘Something Good’ to hide Andrews’ hysterics.

10. It is the third-highest grossing film of all time

Adjusted for inflation, The Sound of Music comes in third behind Gone with the Wind and Star Wars to have collected more than $US1.1 billion. According to boxofficemojo.com: