The final expansion. The Boiler Room and Engine Rooms were combined to make a large room for new oil fired generation equipment, and an exhaust shaft added. A new oil store was added to the left of the entrance. The Observation Post of the old Submarine Mining Station was remodelled, and a new store added opposite the Test Room. A ladder to the surface was added at the side of the Test Room. A long staircase down to the tip of Siloso Point was built, leading to the OSO A.M.T.B. Battery.
The owners of the Fort call this a tunnel complex, but the passage is open to the air, so it cannot be a tunnel. The rooms themselves are earth covered. Today there is a roof over the passage to keep visitors dry. There was no roof originally.