Twice the sealanes of the Atlantic were endangered by German submarines known as U-Boats.

Twice the threat was defeated.

And twice, the vanquished U-Boats arrived at the Portsmouth Naval Shipyard to be carefully inspected, dismantled, and disposed of. It was the ideal place to do so, since the yard was a leader in submarine design and construction, and the naval prison provided a good place to hold the U-Boat crews.

Only one U-Boat arrived in Portsmouth following World War One - a typical example of the U-Boats in service at the end of the war. The shipyard learned a great deal from her technology, leading to the development of the "Portsmouth Compressor", a device American submarines used for two decades to blow ballast in order to surface. After inspections, this U-Boat was taken on a war bond tour before she was sunk in Lake Michigan in compliance with the terms of the peace treaty.

World War Two saw more effort put into thwarting U-Boat activities along the Seacoast, since the Nazi U-Boats had a much greater range than their predecessors. A tower on Appledore Island at the Isles of Shoals was built to keep watch for the submarines and enemy vessels. The stacks of decaying pilings you see between Kittery Point and Wood Island were part of an anti-submarine net to keep U-Boats out of the port of Portsmouth. Three lines of mines and another anti-submarine net guarded the main passage into the Piscataqua River.

Despite all these defenses, U-Boat captains would boast that they knew their way to the shipyard when their submarines were brought in to surrender. Added to the intrigue was a mysterious explosion of one of the mines guarding the harbor in late 1943, followed by a still unexplained salvage operation off Hampton Beach shortly thereafter.

In all, some nine U-Boats arrived in Portsmouth, where American engineers could discover the secrets of German technology before the U-Boats were destroyed as required by the peace treaty.

The most enigmatic of the these was the U-234.

The 1600 ton U-234 was among the largest in the Nazi fleet, and the largest to arrive in Portsmouth. A Type X minelayer, this 305-foot submarine could carry 45 mines which could be deployed while it was submerged. However, laying mines was not its final wartime mission when the large sub surrendered to the Allies.

Rather than a cargo of mines, the U-234 was carrying something far more valuable- assistance for Nazi Germany's lone surviving ally, Japan. Tubes which would normally hold mines were filled with precious cargo. Extra fuel tanks were added to extend the submarine's impressive range enough so it might make the arduous journey across the globe from a besieged Europe to a blockaded Japan. A snorkel had also been fitted on the sub to permit the running of engines underwater, although it didn't supply air to the most important part of the submarine -- its crew.

On board as passengers were two German scientists, three Luftwaffe generals, and two Japanese naval officers. For cargo, the U-234 carried a disassembled jet fighter, which Japan hoped to copy and deploy against overwhelming American air power. Radar and other technological innovations from the Nazi Reich formed part of her cargo. Plans for some of Germany's latest weapons were included on microfilms, making the submarine an archive of Nazi Germany's technological triumphs.

Raw materials were also on board. Mercury, an important war material, was used as ballast rather than lead. More ominously, the U-234 was carrying 1,000 pounds of uranium oxide, about one-tenth of what is needed to construct a working atomic bomb.

Word of the German surrender came as the U-234 was en route to Japan. Rather than risk destruction, she surrendered to the allies. Predictably, the two Japanese officers committed suicide, but the rest of the submarine's crew and passengers were interred at the Naval Prison.

Workmen began the long and intense effort of dismantling and examining the submarine and its contents Apocryphal tales of workmen examining the submarine who found the uranium 235 sealed in steel cylinders made the mistake of ignoring the warnings of these prisoners, and cut the cylinders open and handled the hazardous material. Those who did developed black spots on their hands, and a few would develop leukemia or cancer. Of course at the time, the dangers of radiation were largely unknown, and news of the submarine's atomic cargo was kept secret as a threat to national security. In fact, uranium oxide had often been applied to U-Boat guns during the war to help prevent rust.

The final disposition of the uranium oxide after it was unloaded from the sub remains a mystery to this very day.

The U-234 was examined from top to bottom tested, stripped of her cargo and technology, before she was taken out and sunk at sea by the USS Greenfish. She sank in 500 feet of water between the Isles of Shoals and Jeffery's Ledge.

While the U-234 gained to most notoriety due to its final mission and cargo, other U-Boats were closely scrutinized as well. U-3008, one of the last and most advanced of the U-Boats built was briefly operated by the U.S. Navy to fully evaluate her capacities. While her technology was advanced, it wasn't quite perfected, and she was decommissioned in 1948.

The peace treaty decreed that all U-Boats surrendered to the Allies at the end of World War Two be destroyed though - and so they were either sunk off the coast, or scrapped. All save one.

The U-505 was a typical U-Boat in every way, save one: it was the first ship captured by the United States Navy on the high seas since the War of 1812. The intelligence bonanza from her seizure in mid-1944 was priceless, and since she was captured, and not surrendered, she was deemed exempt from the treaty. Sadly, you will have to go to Chicago to see her on display, where she is on permanent exhibit