Although the source of the artifact is not yet confirmed, a press release from the Navy indicates that “the object appeared on the west coast of Bainbridge Island, was round and very rusty, with rods protruding from its surface. It was moored and had decades of marine growth.
After the naval officers discarded, because of the danger involved, the idea of towing the explosive device to the coast for further study, it was decided to detonate the mine in waters near Keyport, confirmed an officer of the Navy.
The video below shows by way of example since the detonation was not registered at this time, what is the explosion of one of these devices:
The United States Coast Guard also arrived at the site to collaborate with the US Navy; they created a security cordon of almost 1.5 kilometres around the mine, which was near a polygon of the Kitsap naval base.
Source: LT Latercera