Aside from the flooded areas I have also looked at some of the less visited parts:

 

AIR INTAKE DUCT

There are two of these, running from mid height of the Sally Port through to the aft end of the engine room. While I looked through the starboard duct the Sally Port and engine room pics are from the port duct.

Warning: I accessed the duct by rigging a rope from above. While the port duct has the ladder remaining due to rust its strength is unknown and a step may suddenly break - do not use it.

 

Sally Port, showing the outline of the old external 'stairs' and the port intake

Inside the duct - not wildly exciting.

Near vertical shaft down to engine room.

View up from engine room - the ladder is far better preserved on the port side.

CABLE JUNCTION ROOM

This is accessed by short shaft just to the left as you enter the fort. I would like to say I got inside but a decision to try out a tape ladder (rather than using rope descender/ascender) turned out to be a mistake. First time use in the dark is not recommended, and I now know why cavers use aluminium ladders.

View from the Sally Port - it is the first entrance on the left.

Cable tunnel - you see and hear the water moving in and out.

LUB OIL TANK ROOM

Just a small room, with a second store room at far back of engine room.

Facing forward - remains of the two tanks with door to storeroom to right.

The ceiling mirrors the slope of the entry passage.

The storeroom - looks like someone has been assessing its rebar value.

Richard West

FURTHER RESEARCH COMMENTS

While my determined companion Fireball was paddling about in the bowels of the Fort which provided us with these rare glimpses, I was left to do more conventional exploring befitting that of a first timer.

I do want to share some glory as shown in the accompanying photo.

They are under the partially collapsed ceiling between the main batteries on the lower level and many of the more experienced visitors of Drum are familiar with them.

The 14" projectiles are of course armour piercing and not high explosive, which makes sense as these AP projectiles would have been of little use if not against ships.

Fireball accidentally discovered them while we were examining the smaller badly corroded projectile located along the walkway, which is well known, and is an HE; it's fuse now missing.

Conrad Buehler