But movie productions have suffered other disruptions. Among these on a mass scale were strikes organised by various unions and employee groups.

Animators at the Fleischer studio went on a five-month strike in 1937 for better pay and conditions and the Screen Cartoonists' Guild was formed the following year. The non-unionised Disney studio animators went on a five-week strike in 1941. Many animators were fired or left (some formed their own studios) but the studio became unionised and Disney was pressured into recognising the guild.

Interestingly, a big strike was led by Ronald Reagan in 1960 when he was president of the Screen Actors Guild. During his first period (1947-52) as SAG president, Reagan - then a liberal Democrat - had helped get residual payments for TV actors. But film actors were still shut out of residual payments when their films were screened on television. By the late 1950s the actors wanted action on this but producers, unsurprisingly, were reluctant.

In February, 1960, Reagan asked the SAG membership for authorisation to call a strike - unprecedented in Hollywood history. It began on March 7, bringing film production to a halt. Weeks of negotiations with producers followed and a settlement was reached on April 18. It gave actors residuals for films made from 1960 onward but not those made before 1948. There was also a one-off payment of $2.25 million for films between 1948 and 1960 that was used by the guild as seed money for health and pension plans.

While not all actors were happy with the plan, it was endorsed by the vast majority of members and paved the way for future strikes in the movie industry.

Reagan's stance on unions - at least American ones - changed somewhat when he became a Republican California governor and president.

For example, as president he fired thousands of air-traffic controllers who had gone on an admittedly illegal strike and, rather less defensibly, appointed three management representatives to the National Labor Relations Board (NLRB), leading to a significant departure from its obligation under law to help promote collective bargaining, among other things.

Back on topic: on "Hollywood Black Friday" - October 5, 1945 - a six-month strike by set decorators represented by the Conference of Studio Unions reached a violent climax.

An encounter at the Warner Bros studio gates involving picketing strikers, strike breakers, studio firemen, and police resulted in dozens of injuries.

Negotiations and another strike led to the CSU's power fading to nothing - its members went into another union - and the whole affair helped prompt the Taft-Hartley Act of 1947, limiting the activities and power of labour unions.

Nevertheless, there were several other strikes over the years.

In 1958, the American Federation of Musicians called a strike against Hollywood studios. Many California musicians were unhappy with the AFM's leadership - it took big fees for a general musicians' trust fund favouring the many part-time players across the country at the expense of the Hollywood professionals. AFM policies also discouraged television producers from scoring in Hollywood so many shows used canned library music recorded in Europe.

The strike meant recording musicians on the West Coast were out of work.

One prominent casualty of this was composer and conductor Bernard Herrmann, who was unable to record his score for the Alfred Hitchcock film Vertigo: it was recorded in London and Vienna under the baton of Muir Matheson (Herrmann was not happy with the results).

A breakaway union - the Musicians Guild of America - was formed and won the right to negotiate.

While MGA musicians got more TV music work, the studios, then undergoing other major changes as the old-style studio system was breaking up, dismantled their music departments and employed musicians on a freelance basis.

Without a good script, you can't have a good picture, but despite this, writers are frequently the butt of jokes and put-downs, are easily replaced, and don't have the strongest bargaining position.

The Writers Guild has had strikes in 1960 (21 weeks), 1973 (three-and-a-half months), 1981 (three months), 1985 (two weeks) and 1988 (22 weeks) and 2007-8 (14 weeks).

The Directors Guild has had one strike, in 1987, that lasted just over three hours.

Since these strikes all tend to be over disagreements about payments - residuals, new media - it seems like the relative status of directors and writers remains the same.