During that era of undersea exploration, only two submersibles--Aluminaut and Alvin--were capable of operating at the extreme depths needed for a number of missions.

Two of Aluminaut's most notorious missions were rescuing the smaller Alvin after it sunk in 1969, and assisting Alvin in the search and retrieval of a loose U.S. Air Force hydrogen bomb in 1966.

The errant H-bomb was one of four aboard an Air Force B-52 bomber when it collided with a KC-135 tanker near Palomares, Spain. Three of the bombs were located on land, but the fourth was seen parachuting into the sea.

A huge search, highly publicized, was launched. At that time only Alvin and Aluminaut were capable of operating in the oceanic depths where the bomb was believed to be. It was described as far more challenging than finding the proverbial needle in a haystack.

Aluminaut discovered wreckage from the downed bomber, helping Alvin to eventually find the bomb itself.

More than three years later, in mile-deep water off the coast of Massachusetts, Alvin was lost when a cable snapped as it was being lowered into the water. Fortunately, the three-man crew was able to scramble to safety before the craft flooded and sank.

At that time there was only a single craft capable of attempting to rescue the valuable submersible from such deep waters: Aluminaut.

It was a major effort. A first dive failed when a piece of essential special equipment failed. It was redesigned and, once more, Aluminaut's crew descended to the ocean floor. This second attempt was successful and Alvin was able to be craned to the surface and secured.

Alvin is still being operated by the Woods Hole (Mass.) Oceanographic Institute,

Aluminaut, retired in 1971, was given to the Science Museum by Reynolds Metals, its owner, in 1995.

The large, orange undersea craft looks like something out of a Jules Verne novel. If you wish to explore and examine it, you may have to ask someone how to find it.

It is well worth it.

Armchair Adventures/Plus is now up and running. Check it out: armchairadventuresplus.blogspot .com.

Paul Sullivan of Spotsylvania County, a former reporter with The Free Lance-Star, is a freelance writer. Email him at PBSullivan2@cs.com.