I was a Navy OT A during the Cold War. I worked in the SOSUS community meaning my shipmates and I detected and tracked submarines day in and day out. The fact that it was a small vessel could have made detection of an implosion more difficult. But most definitely not impossible. They also had the last known coordinates which helps triangulate location and a search area for debris fields. This was always something we trained for and hoped to never see an implosion in real time. Sadly, this was not to be.