R-15 through R-20
The USS R-15 seen in the Panama Canal. The date is between September 1918 and December 1918 when she and her sisters R-16, R-17 and R-18 patrolled Panamanian waters in the closing months of WW I.
She is backing away from either a pier or maybe a tender. The exact location is in some doubt, but the area seems to fit the Rio Chagres vicinity with the rail lines in the background and pairs of power poles as a clue.
The WW I time frame is pretty certain due to the fact she is armed with the 3"/23 caliber Mk 9 gun (the gun barrel is mixed in with the legs of the two Chiefs in front of the conning tower), which she carried for only a short time.
After her return from Panama, she and her sisters went to Mare Island to have the small guns removed and get deck modifications to accept the new, much more powerful 4"/50 caliber Mk 9 gun she will receive once she reported to Pearl Harbor.
See More R-15 photos
R-16 (SS-93)
R-17 (SS-94)
R-18 (SS-95)
R-19 (SS-96)
R-20 (SS-97)