In 1885, the Fort was marked for significant changes to the armament. The 64 Pounders were to be retired from service, and a new emplacement with a Mark IV 9 ·2 Inch BL Gun with an underground magazine would be constructed. The magazine held 100 rounds of ammunition. This gun would give the Fort much needed increased hitting power, and at a greater range.
Another 7 Inch RML Gun with an underground magazine and store room would give added cover to the south from atop Mount Siloso. A Look Out Post would also be constructed on Mount Siloso near the new 7 Inch RML Gun Emplacement. The new guns are shown as the No.3 and No.5 Guns in the plan. The No.3 Gun is the 9·2 Inch BL Gun.
The Mark IV 9·2-Inch Gun emplaced at Fort Siloso was one of five Mark IV 9·2-Inch Gun which were deployed in Singapore. Two of the others were emplaced at Fort Connaught, with the other two going to Fort Pasir Panjang (renamed Labrador during the 1930s). The Pasir Panjang No.2 9·2 Inch Emplacement with its magazine still exists, although there is no access to the magazine. The Pasir Panjang No.1 9·2 Inch Emplacement was destroyed to install two 6 Inch BL Guns in the 1930s. Its Magazine remained and was modified to service the 6-Inch Guns of the Labrador Battery. There is no access to this Magazine. Nothing remains of the two emplacements at Fort Connaught.