English: Tubes in front are a anti-submarine mortar launcher from a old ship. Building in back is the Battery Observation Post.

With the fear of German invasion of the British Isles, Sydney became the home of the Royal Navy. Fort Petrie Military Museum honours this period, and is one of seven fortifications that were located along Sydney Harbour during World War II. Strategically located as an observation post, Fort Petrie offers powerful views of Sydney Harbour and into history that should never be forgotten.

The Fort Petrie battery was constructed in 1939-40 at a cost of $105,000 dollars. It was decommissioned in October 1956 more than fifteen years after the first convoy departed.

The building of the shore batteries in Sydney Harbour insured as safe anchorage for the thousands of merchantmen that would sail in great convoys to Great Britain. Sydney, was also a major producer of steel and a centre for the distribution and production of coal; both very important war-time commodities.

It was construction at a hectic and feverish pace. Also in 1939-40 construction began on a series of fortifications to defend Sydney Harbour against a German attack.

In three months of operation, 967 ships had sailed in 48 convoys out of Sydney Harbour. The last convoy, left on May 26, 1945, with its lights on.

There were 7 buildings on site, all housed underground, except for the Battery Observation Post

The Underground consisted of the Officer's Mess, magazine, gun watch and artillery stores, bathroom and showers, educational and recreation room. These were all heated by electric heaters.