You are correct about the MK 14 Fire Control Director. Routine filtration system was an air, color-coded. However, the US NAVY upgraded the MK 14 to MK 51ís at the end of the war and USS LST-325ís was changed out to MK 51 (similar in appearance only) and was transferred to the Hellenic Navy with Mark 51ís (located in both Tub's)---and N2 was used for preventive and repair maintenance of humidity, etc...(regardless of the filtration system). See Navy Intel Records below.
In addition, I would agree with your assessment that N2 was used for Fire Suspension. I just love the navyese talkÖ.I can feel the deck moving. thank you.
USS LST-325 (RHS SYROS L144)
Specifications: (as reported by Office of Naval Intelligence-1945)
Displacement 1,625 t.(lt), 4,080 t.(fl) (sea-going draft w/1675 ton load)
Length 328' o.a.
Armament (varied with availability when each vessel was outfitted. Retro-fitting was accomplished throughout WWII. The ultimate armament design for United States vessels was
2 - Twin 40MM gun mounts w/Mk. 51 directors
4 - Single 40MM gun mounts
12 single 20MM gun mounts
Propulsion 2 General Motors 12-567, 900hp diesel engines, 2 shafts, and twin rudders