 The current route of SR 308 was first added to the state highway system in 1929 as the Keyport branch of State Road 21 and was carried over to the primary and secondary state highway system in 1937 as a branch of PSH 21 . The branch traveled 2 @.@ 34 miles ( 3 @.@ 77 km ) east from PSH 21 near Naval Submarine Base Bangor to the Naval Undersea Warfare Center in Keyport , intersecting Secondary State Highway 21B ( SSH 21B ) before crossing Liberty Bay . The Keyport branch was incorporated into SR 303 , which replaced SSH 21B , with a short spur route serving Keyport . SR 308 was established in 1971 to replace the Keyport spur of SR 303 and extended over SR 303 in 1991 to SR 3 after SR 303 was moved south to end in Silverdale . 
