Read this and answer the question. If the question is unanswerable, say "unanswerable".

In 1958 as part of an experiment, Operation Argus, the United States Navy detonated an atomic bomb 160 kilometres (100 mi) high in the upper atmosphere about 175 kilometres (109 mi) southeast of the main island.

What was detonated during Operation Navy in 1958?
unanswerable