Navy Blimp Crashes In San Francisco Neighborhood

A blimp crashed near San Francisco, with its crew missing. The blimp's gondola, still carrying a depth charge, rolled onto electric wires and settled in the street without causing injuries. Oil, parachutes, and a life raft were found, but two life belts were missing. The Navy is searching the ocean off the Golden Gate, stating that such an incident has never occurred before.

What was missing that raised concerns during the Navy's search?

How do Navy officials describe the uniqueness of this incident?