Within 30 minutes, a different, non-nuclear civilian construction group began an assignment to bring Guitarro within a half-degree of trim; this entailed adding water to the forward ballast tanks to overcome a reported two-degree up-bow attitude.

At 19:45, the non-nuclear group stopped adding water to the ballast tanks and began to halt work for their meal break, leaving at 20:00.

At 20:55, Guitarro sank, leaving only her sail above water, earning her the nickname "Mare Island Mud Puppy".

The construction crew put a fire hose down the tank's vent pipe and forced it past the check valve.

[2] The Congressional report concluded that the sinking was caused in large part by "the action, or inaction, of certain construction workers who either failed to recognize an actual or potential threat to the ship's safety or assumed that it was not their responsibility."

In the mid-to-late 1970s, Guitarro was stationed at Point Loma in San Diego, California, commanded by Alvin H. Pauole, followed by Scott Van Hoften.

Her scrapping via the Nuclear-Powered Ship and Submarine Recycling Program at Puget Sound Naval Shipyard in Bremerton, Washington, was completed on 18 October 1994.