- "This was your grandfather's. He was one of the Navy's first frogmen during World War II. He was so stealthy in the water, his unit nicknamed him Manta. But after the war, his country forgot about him. So, he went back to the sea, scavenging and surviving with his wit... and this knife. He gave it to me when I was your age. And now it's yours, son."
- ―Jesse Kane to David Kane about the knife of his father.[src]
The grandfather of David Kane fought in World War II as one of the Navy's first "frogmen" (code-named "Manta" for his stealthiness). It is not known how well he performed, or what exactly he did during the war, but based on Jesse's testimony, his deeds apparently earned him the respect and admiration of his peers.
After the war ended, however, his country decided to forget about what he'd done during the war; and thus, he returned to the sea and survived by scavenging and using his wits. Eventually, he had a son with a unknown woman and named him Jesse. When he attained a certain age, he gifted him his special knife.