Now I am back from holiday so:
- That superstructure you have in front of the Terne III launcher is the 3" main gun magazine on the Oslo class.
- Terne III needs three deck, you can do it by only two deck but then you have only enough ammo for launch for 3 maybe four attack. (Terne III have six rockets in it's launcher, When attacking and submarine it's launching 3 three rockets to make an ring around where the submarine are, The in build magnetic sonar will detonate the explosive when it detect the submarine are one the same depth to it (all six Terne III will explode almost on the same time (death zone)). That is just one attack, it would have to reload before it can do it again.
I have got some newer information of what stands here, that information says the system is much larger than I have drawn it to be on this drawing.
The Terne III is light compared to other ASW systems, But it took a lot of space, that is also why Norway used the 3" american gun without no bellow deck loader, only loading from ready magazine aft of the gun (Manual loading, WW2 style!)
Terne III consist of the launcher up on the deck with six ready and almost always armed rockets (Specially on patrol), the deck bellow have an carousel with five rockets and one rockets free on the deck that have to be loaded up manually, on the same deck you have the main controller for the system, the deck bellow of that have two carousel with either five or six rockets each (all rockets in these carousel are ready for use, the last armament will be done electronic (if it works) when it have come up in the launcher), The last deck have the main magazine where all the rockets are stored. On Oslo If I am not wrong they had 4 ready rounds (24 rockets) and around 48 to 84 rockets stored in the magazine, and some stored in various location around the ship.
Totally the system consist of three deck with Terne III weapon system, large and powerful sonar in the bow, where the electronics are taking up almost all the space in the bow together with the Terne III, Terne III reach from the Sonar and aft to the ship sickbay, There is also an secondary magazine for the main gun there to.