This is TARPON (SS-175) in October 1942 after a refit period at the Mare Island Navy Yard. The boat is camouflaged in the overall black (BK) of Measure 9.
This refit cut down TARPON's sail aft, reducing the silhouette of the boat - this modification would be applied to almost all of the pre-war submarines during their refits. As the war progressed, all of the surviving PORPOISE/SHARK class boats eventually had their sails reduced both fore and aft. A 20mm Oerlikon has been mounted on the cigarette deck aft. Large and prominent covers for the engine mufflers are visible aft as a raised portion of the deck aft of the 3"/50-cal gun. Perhaps most importantly, this refit added radar -- an SJ surface search set is bracketed on a pole mast to starboard of the periscope shears, and the forward periscope has been replaced with a telescoping antenna mast for the SD air search antenna. The periscope shears have been cut back as well. Later refits would strip these down even further.
A common complaint about the pre-war PORPOISE/SHARK and SALMON/SARGO class boats was the presence of only four torpedo tubes forward. Early war refits attempted to address this by adding two external torpedo tubes just above the bow anchor positions on six of the PORPOSE/SHARK class boats. These tubes could not be reloaded at sea, were difficult to maintain, and subject to damage under depth charge attack. Not considered successful, most installations were removed in later refits.
TARPON would serve throughout the war in the Pacific, completing 12 war patrols before being reassigned to the US east coast. The boat survived the war, serving as a training submarine in the 1950s, before finally being sold for scrap in 1957. TARPON foundered in deep water off Cape Hatteras while being towed to a scrap yard, and the wreck is now a diving attraction.
