I’ve driven by it a million times in Morro Bay, CA and finally decided to look it up. Looks like it was built to rescue crews of “sunken” or disabled submarines
DSRV Avalon -- Pioneer of Submarine Rescue -- Morro Bay, CA
The DSRV Avalon submarine rescue ship is on display at the Central Coast Maritime Museum in Morro Bay, California. It launched in 1960 during the Cold War.