Doug Allan

But the available equipment is heavy and restrictive.

Cousteau and his colleagues test these early designs, but their shortcomings quickly become clear.

In one experiment, Cousteau loses consciousness after breathing an unsafe level of oxygen.

Another key challenge is that divers must manually regulate the flow of air from the tank, releasing it in careful bursts.

What is needed, Cousteau believes, is a mobile device capable of adjusting the airflow automatically.

The possibility of moving freely beneath the surface becomes a burning ambition.

But in September 1939, the wider world has more urgent plans.

Germany invades Poland, and France, alongside Britain, declares war.

While his friends are reassigned to duties in other parts of the country, Cousteau remains stationed at Toulon.

In May 1940, France is invaded by the Nazis, with whom the French sign an armistice the following month.

With German troops occupying Paris and the north, the government retreats south.

For Cousteau and Simone, these anxious times are lightened by the happy arrival of their second son, Philippe, named after his father's good friend, Philippe Tallier.

A couple of years later, Cousteau is posted to a base in Marseille.

That spring, he finds a 35mm movie camera in a junk shop.

With help from his friends, he begins adapting it for use in the sea.

That summer, reunited with his family and the sea musketeers, Cousteau works on a film capturing his friend's spearfishing, which he titles 18 Meters Down.

But in November, Cousteau and his family are woken in the night by the roar of airplanes overhead.

On the radio, they learn that Adolf Hitler has ordered the invasion of southern France.

German and Italian forces are now moving in.

In response, the French navy scuttles its own fleet on the southern coast to prevent the ships from falling into enemy hands.