Hans Spear is an obvious allusion of Albert Speer who was the German Minister of Armaments and War Production and was tried and convicted of war crimes.
While talking with Klink about the new factory, Klink mentions that before it became a cannon factory it was used for the manufacture of a "small car". Of course, he probably was talking about the Volkwagon Beetle, which gained popularity in the U.S. after the war.
Per the title, the swing shift was the shift at a manufacturing plant between the day shift and the "graveyard" shift that started at midnight.
Guest star Hal Smith who played Hans Spear played town drunk Otis Campbell on The Andy Griffith Show.
The cannon barrels appear to be barrels for 20MM guns.