In 1906, something unusual appeared in the sky above Queen's Road (today's Queensway). Newspapers at the time reported it as an 'aerial ropeway', or 'overhead railway'. Today we'd call it a cable-car.
Here's the approximate route that it followed (click '+' to zoom in for a better view):
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- A - "The Aerial Rope-way starts with a station on the sea-front of the Ordnance Department's Yard, where two small manual cranes will deliver the stores from a lighter direct onto the cars standing, or rather hanging, ready in the station." 
- B - Power-house (engine room) and Central Station
- C - Station at north-east corner of the Magazine
- D - Station at the Explosives Laboratory
A Navy project?
I usually think of the old military cantonment roughly split into Navy north of Queen's Road, and Army to the south. However a detailed map of the area  shows that the thin strip of land below the path of the cable, the magazine, and the Explosives laboratory all had Naval Boundary Stones marking their boundaries. Was this the main magazine for the Navy, and they built the cable-car built to give easier access?
How long did it last?
Based on the newspaper article, I'll guess 1906 as the date it was built. Then there's a map dated 'c.1924'  that shows it still in existence. But when was it demolished? By the second world war there was a large magazine at Little Hong Kong. If that replaced this magazine, the cable-car may have gone out of use at the same time the magazine was relocated.
There were two types of car that ran along this route "one of open round-bottomed tray shape, for carrying large shell, and the other closed cylindrical for ammunition and explosives." Can you imagine high-explosives running to and fro across Queensway today? (And especially with the recent memory of the falling Ngong Ping cable car!).
Has anyone seen it?
I haven't noticed it in any old photos from the early 20th century. But then I didn't know to be looking for it. If you fid any photos that show it, or have any information to share, please could you let us know in the comments below?