Be honest now. Were you one of the people who kept Titanic on top of the box office for 15 weeks? When did you first cry? At Gloria Stuart's old Rose talking about the people who died? Or the captain standing at his wheel while his ship went down? Did you consider buying a replica of Rose's Heart of the Ocean necklace? And, most pressingly, are you convinced that Jack could have survived if only he'd shared that board with Rose?

Never mind the face that launched a thousand ships, Titanic — which celebrates its 20th anniversary this month — was the ship that launched a thousand crazes, turned Kate Winslet and Leonardo DiCaprio into heart-throbs, and made the world wild about naval tragedy.

Titanic's US$2 billion-plus box office record has since been beaten, but the film — a blend of special effects spectacle and old-fashioned romance, powered by the genuine chemistry of its stars — is still without equal. With Hollywood now obsessed with sequels and existing intellectual properties, it's hard to imagine any studio agreeing to spend all the money in the world on an original story of such ambition and scale. It conquered the world, yet Titanic was so nearly an utter disaster.

The film told the story of poor itinerant artist Jack, and Rose, a society girl whose widowed mother is marrying her off for money. They meet and fall in love on the doomed ship. Titanic was the most expensive film ever made at the time: an apparent fool's errand for action director James Cameron.

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The shoot was riven with problems. The budget spiralled to US$200 million, leading to predictions that the movie would be a complete turkey. This wasn't helped by production delays and Paramount pushing the release back by six months. Cast and crew, barely getting by on four hours' sleep a night, caught colds and infections from prolonged periods in the water tanks.

So it was a shock when Cameron's three-hour baby was released and broke box office records. Cinemas physically wore out their copies of the film through overuse, and Titanic won 11 Oscars. The director really was the king of the world.

At a time when irony was all the rage in cinema, Titanic was something else: the film's grace is going for simple feeling over schmaltz.

That first half is a film in itself; a gorgeous, charismatic romance in impeccable period surroundings, before launching into the harrowing devastation of what happened after the ship hit that iceberg. The quarter-hour that bridges the two is agony, even before Rose goes down to the suddenly flooded E deck to rescue Jack and she, and we, suddenly realise how dreadful a situation this is. First-class passengers serenely drink brandy while third-class are forbidden from climbing the stairs — Cameron's unflinching eye has us bear witness to it all, and then kills off Jack to boot.

Winslet's vivacious performance scored her an Oscar nomination, but poor Jack's noble sacrifice didn't butter any parsnips with the Academy. When news of DiCaprio's snub broke, it was contacted by more than 200 people demanding a recount. (DiCaprio quickly recovered; his US$2.5 million Titanic salary ballooned to US$21 million for his next film, The Beach.)

web pages, still relatively new in 1998, were built by fans to show how much they adored DiCaprio, Winslet — and Celine Dion.

James Horner's score, and his song for Dion, My Heart Will Go On, played no small part in sending Titanic stratospheric.

In 2012, Entertainment Weekly observed that Titanic was the first film to fall victim to online "hater culture". It was, wrote critic Owen Gleiberman, "a huge, powerful, ambitious movie, by a geek-god film-maker, that actually dared to be innocent about love. For if there's one thing that internet culture, with its immersion in hipness, control, technology, and a certain masculine mystique that binds all those things together, cannot abide, it is romantic innocence".

Titanic fans' ardour can seem a bit extreme to the uninitiated. An internet theory, showing how Jack and Rose could both have fitted on that board in the icy Atlantic, was so hotly contested that the TV science show Mythbusters debunked it, concluding that it could only have been possible had they used Rose's life jacket for buoyancy.

"I think it's all kind of silly, really, that we're having this discussion 20 years later," Cameron told Vanity Fair last week. He added: "But it does show that the film was effective in making Jack so endearing to the audience that it hurts them to see him die. Had he lived, the ending of the film would have been meaningless ... The film is about death and separation; he had to die."