longest career by a U.S. skipper?

[WernherVonTrapp]

The longest certified career as a submarine captain is 18 years 9 months 26 days and was achieved by Wonjang Kim and Kwanghyun Kim (both South Korea) as of 17 October 2007.

The longest submerged and unsupported patrol made public is 111 days (57,085 km 30,804 nautical miles) by HM Submarine Warspite (Cdr J. G. F. Cooke RN) in the South Atlantic from 25 November 1982 to 15 March 1983.

Most successful submarine commander was
Lothar von Arnaud de la Perière (the captain of the German submarine U-35) fought in the German Imperial Navy in World War I, during which he sank an astounding 194 ships with a total tonnage of 454,000 Gross Registered Ton (GRT). In many cases the vessels were unescorted merchant ships, meaning that the submarine's crew would board the vessel, inspect its cargo, and allow the crew to board lifeboats. It would then be sunk using the sub's 88 mm (3.5 in) deck gun to conserve torpedos.

The largest target ever sunk by a submarine was the Japanese aircraft carrier Shinano (72,890 tonnes or 160.9 million lb), sunk by USS Archerfish (Cdr Joseph F. Enright, USN) on 29 November 1944.

Largest gun on a submarine:
The three British Royal Navy M Class submarines (M1-3) developed towards the end of the First World War were fitted with a deck-mounted 30.48-cm (12-in) gun, a weapon more commonly found in turrets on battleships. The diesel-electric powered submarines were 90.5 m (297 ft) long, had a surface displacement of 1,600 tonnes (3.5 million lb), and could travel at 8 knots (15 km/h or 9 mph) submerged and at 14 knots (26 km/h or 16 mph) on the surface.