Short answers, pulled from the story.
The S-II was the second stage of the Saturn V rocket, built by North American Aviation. Five J-2 engines in a quincunx formation burned liquid hydrogen and liquid oxygen to generate one million pounds of thrust, pushing the vehicle through the upper atmosphere.
North American Aviation was awarded the S-II contract on the 11th of September 1961. The manufacturing plant was built by the government at Seal Beach, California, and the contract called for fifteen flight stages. North American also held the contract for the Apollo Command and Service Module.
The S-II's common bulkhead was a shared wall between the liquid oxygen and liquid hydrogen tanks, made from two aluminum sheets separated by a honeycomb of phenolic resin. It eliminated the need for a separate intertank section and saved 3.6 tonnes in weight. The bulkhead also insulated a 126-degree Fahrenheit temperature difference between the two propellant tanks.
Each of the 12 gores forming the LOX tank wall was shaped by placing it in a 211,000-liter tank of water and setting off three carefully orchestrated sets of underwater explosions. The water transmitted the blast force evenly across the metal to press each gore into the required curvature.
S-II-2 on Apollo 6 suffered two engine failures during ascent due to pogo oscillation damage from the first stage and incorrect engine control wiring. S-II-8 on Apollo 13, which launched on the 11th of April 1970, lost its inboard engine during ascent due to pogo oscillation.
S-II-13 launched Skylab 1 on the 14th of May 1973 and became the only S-II stage to enter Earth orbit. The interstage failed to separate due to payload damage during launch. The stage made an uncontrolled reentry into the Atlantic Ocean on the 11th of January 1975.