Via a story on NPR’s All Things Considered (last story on the page: audio link) the intrepid research submarine Alvin is going to be replaced with a larger sub capable of deeper dives and longer stays at depth.

Alvin is a truly storied scientific instrument, one of those few machines that almost singlehandedly revolutionize a scientific field. I’m looking forward to seeing what her successor will do.

This post isn’t entirely about the excellence of Alvin – I also have a little bit of an axe to grind. Let me point out that, in this day of submarine ROVs with ever increasing capabilities, the thing that oceanographers and deep ocean biologists want is a machine that will enable them to go in person into the depths. A dive in the new sub will take up to ten hours, cramped up in a space about the size of the interior of a VW beetle, with all manner of projections and angles to increase the discomfort. Internal temperatures during a dive hover in the neighborhood of zero celsius, and if something goes seriously wrong, you die. Much better to send a machine, don’t you think? But no: the people best equipped to make the judgement, the people who will be trading sitting in front of a computer in a climate controlled room, sipping fresh brewed coffee for a cramped, cold, dangerous machine that will put them right next to what they want to study – they choose the sub. Why? because you simply do better science on site than you can remotely, and it’s going to be that way for the foreseeable future. The lessons for space exploration should be obvious. I’m looking at you, Bob Park.

Dismounting my hobbyhorse and returning to Alvin, there’s an interesting story in the book Water Baby. When Alvin was under construction three pressure spheres were made and tested. The best (no. 2) was used on the sub, and sphere no. 1 was to be tested to destruction. The test vessel was a large oil filled tank which could be pressurized to simulate dives to various depths. The 40,000 pound lid of the vessel screwed into place on top. The crush test of sphere no. 1 was also going to be the first test of the pressure tank above 4000 psi. From the book:

At 4300 psi there was an explosion. In the next second the engineers calculated the probable trajectory of the tank’s lid, concluding that 40,000 pounds of steel were headed for the tin roof above them. They ran, all of them headed at once to the only other door at the far end of the building. “I remember the instantaneous transport of myself, like a Tibetan monk using the mind to will myself out of that building” Walsh said.
[…]
The super tank looked oddly untouched and its 40,000 pound lid, undamaged, was in place. The deadman was broken and its 40 foot cable was gone. When they removed the cover, they saw that the shrapnel had come from the upper threaded portion of the tank. The lid had shot up at least 40 feet and dropped back onto the tank, driving it about three feet deeper into the ground.

In the tank sat sacrificial sphere no. 1 undamaged.

The test tank failed at a pressure equivalent to 9600 feet, testing the sphere judged to be of the lowest quality.