On March 25, 1915, the submarine USS F-4 slipped beneath the waters off Honolulu, Hawaii, for what was supposed to be a routine training dive. She never came back. When she failed to surface, anxiety quickly turned to dread. The Navy had lost its first submarine at sea with all hands aboard. The disaster was not only a human tragedy, it was also a crisis for a service that was still experimenting with the strange new world of undersea warfare. Submarines were only beginning to find their place in naval strategy, and to lose one so suddenly and completely raised difficult questions about their safety, their reliability, and their future.