Alexandra Observing Station and Test Room for a controlled minefield was built to the rear of the battery on a small knoll. The Mine Control Station was for mines laid in the Narrows Channel to the front of the battery.
The Observing Station is entered through a passageway over 50 metres long that leads underground. The Test Room is some 25 metres underground, protected by a concrete roof and then earth. Stairs lead up to the Observing Station from the Test Room. Work on the complex commenced on the 23rd June 1886 and the work was completed on the 21st November 1888. The cost was £250, about half the estimated cost.
A small accommodation unit was built close to the Observing Station. This building was authorised on the 14th January 1891 and the work started on the 18th April 1891. The building was completed on the 30th January 1892 for a cost of £190. This small building has a kitchen, bedroom and 1250 galleon water tank. At one end of the building was a small office with Observing Room on the mezzanine level and a Test Table on the ground floor. The ruins of this building survive.
This is probably one of the best preserved submarine mining observation stations from this period.
Some images courtesy of Martin Buckley.