The primary cause of the USS YF-415's sinking was a combination of poor weather conditions and structural failure. On December 12, 1970, while the vessel was moored at the Naval Weapons Station in Yorktown, Virginia, it was struck by heavy winds and waves. The ship's hull, which had been compromised, ultimately led to its sinking. The incident highlighted issues related to maintenance and the ship's seaworthiness at the time.

For more detailed information, you can refer to resources discussing naval incidents and the specific events surrounding the USS YF-415.