As a ship enthusiastic railwayman I really like the vessels with their own tracks on board :-) - That would be my place!
Deck picture of "HMS VÄSTERVIK - R136" in the Marine Museum at Karlskrona - 13.07.2015

I suppose, that the rails are to move the torpedeos at different positions to launch them:
See pictures:
http://www.shipspotting.com/gallery/photo.php?lid=2996931
http://www.shipspotting.com/gallery/photo.php?lid=2996933
http://www.shipspotting.com/gallery/photo.php?lid=2996938

https://www.marinmuseum.se/en
https://www.marinmuseum.se/en/museum-ships/the-vastervik-missile-ship
https://sv.wikipedia.org/wiki/HMS_V%C3%A4stervik_(T136/R136)