Standard Landing Craft Unit FOUR (SLCU-4) was an element of Fifth Amphibious Force, Pacific Fleet. Each assault landing ship (APA, AKA, etc.) had one (or more) SLCU's assigned or attached.
A little more on CALVERT (probably more than you need or want). She made one trip to Vietnam just prior to being decommissioned in 1966. Unit and ship's histories are eight dollars each. An 8" X 10" black and white of CALVERT (color unavailable) is twenty-five dollars (this is an actual, studio-quality, official photograph - NOT a print-out).