As new on this board i do not know much of guns but i know a little about ships.
"More puzzling: what is this myterious object on the far right of the top picture? Is it an ammunition storage or some kind of launcher? Never seen anything like that."
I think it is a Hedgehog (Probably an Mk 11) an ASW spigot mortar designed during WWII. The Iranians had it on a few US designed ships that they bought second hand in the 1970s. I think that the other guns besides the 75mm Bofors Mountin guns are naval guns, i think they are US made.