Both are Navy-owned deep submersibles. One was retired in 1963, while the other is still active. But their histories are related.
The bathyscaph Trieste joined the U.S. Navy in 1958. Based at the Naval Electronics Laboratory (NEL) in San Diego, she was deployed to Guam for a series of deep dives in 1959–60 that included one to the deepest place in the ocean.
By early 1961 the NEL team had nearly three years’ operational experience with the Trieste, and much had been learned about this new technique of ocean exploration. While the bathyscaph had no depth limit, it was also very fragile. When fully loaded she had to be towed to dive sites at a stately five knots. Calm seas were a must and not always guaranteed. The paradox was the Trieste could dive at any place in the world’s oceans, but you could not get her to the dive site. It was not until the 1970s that a mother ship (floating drydock) was provided to transport her long distances.
At San Diego each operational dive cycle took about seven days. Most of the dives were to 4,000 feet or less. These “shallow-depth” operations were costly, time-consuming, and sometimes only marginally safe.