The design flaws that doomed the airship USS Akron ZRS 4

The Akron went into the Atlantic off the New Jersey coast in the early hours of 4 April 1933. Seventy-three men died. Three survived.

By loss of life it remains the worst airship accident in history, worse than the Hindenburg, which people find surprising because one of those crashes was filmed and the other happened in the dark at sea.

What she was supposed to be

Akron was not a transport. She was a flying aircraft carrier.

The concept was scouting. The Navy wanted something that could search enormous areas of ocean, and an airship with a very long endurance that could launch and recover its own fighters seemed like a reasonable answer in the 1920s.

She had an internal hangar and a trapeze mechanism. An aircraft flew up underneath, engaged a hook, and was hoisted inside. It worked, and the film of it is remarkable.

She was helium filled, not hydrogen. The United States had helium and used it, and so fire was never the issue with the American rigid airships.

The problems in the design

Structural margin. She was built to be as light as possible because lift is everything in an airship, and the margins against structural loading in violent air were thin. The ring and girder structure was an engineering achievement and it was not conservative.

The tail. The lower fin on the American rigids was large and the control surfaces were substantial, and in Akron's case the tail structure is where the failure began. That is the consistent element in the investigations.

Altitude and pressure. A rigid airship's gas cells expand as she rises, and she has to valve helium off to avoid overpressure. Helium valved off is lift you cannot get back, so every climb costs you buoyancy permanently for that flight. This constrains how a crew can respond to weather.

And the practical one. She carried no lifejackets for most of the crew and no lifeboat. That single decision is the difference between seventy-three dead and a much smaller number, and it is the detail that stays with me.

The loss

She left Lakehurst on the evening of 3 April 1933 to assist with calibrating radio direction finding stations along the coast.

She flew into a severe storm off New Jersey. The accounts describe violent conditions, a rapid loss of altitude, a recovery, and then a second descent from which she did not recover. The lower fin struck the water and she broke up.

The water was cold. Men who survived the structural failure did not survive the sea, and without flotation there was very little any of them could do.

Rear Admiral William Moffett, the head of the Bureau of Aeronautics and the most important advocate for naval aviation of his generation, was aboard and was lost.

What it ended

Her sister, the Macon, was lost less than two years later in February 1935, after a tail structure failure in flight. Most of her crew survived, partly because of lessons taken from Akron.

Two losses of that kind, close together, finished the rigid airship in American naval service. The programme had always been contested and this settled the argument.

Whether the concept could ever have worked is a question people still argue about. My own view is that the scouting role was real and the airship was the wrong vehicle for it, and that carrier aviation and long range patrol aircraft answered the same requirement within a decade without needing to survive a thunderstorm.

Getting it right

She was ZRS-4, rigid airship scout number four. Macon was ZRS-5.

Neither was the Hindenburg, which was German, hydrogen filled, civilian, and lost at Lakehurst in 1937. The three get mixed up constantly because Lakehurst appears in two of the stories.

And the seventy-three figure is the one generally given for Akron. Contemporary reporting varied in the first days, as it always does.