Bombay Castle consists of a submerged reef located between 07°50′N 111°40′E / 7.833°N 111.667°E / 7.833; 111.667 and 07°56′N 111°42′E / 7.933°N 111.700°E / 7.933; 111.700 (between 07°50′N 111°40′E / 7.833°N 111.667°E / 7.833; 111.667 and 07°56′N 111°42′E / 7.933°N 111.700°E / 7.933; 111.700) at the northern end of Rifleman Bank.[3][4] At its shallowest point, it has a depth of 3 metres (9.8 ft) consisting of sand and coral.[5] It is 80 miles (130 km) east of Huyền Trân (Alexandra Bank) and nearly 80 miles (130 km) west of An Bang (Amboyna Cay).[6]
Bombay Castle has a 22.5 metres (74 ft) tall lighthouse on steel pilings that was built in 1995. The lighthouse is two storied, with accommodation for the lighthouse keepers and a dish antenna.[7][8]
In addition to the lighthouse (DK1/21), three other DK1 rigs ("economic, scientific and technological service stations") have been constructed by Vietnam in this area. The current (2015) cluster has 3 rigs in use.
DK1/4: Completed 16 June 1989, was the 2nd DK1 rig completed. It collapsed on the night of 4 December 1990 during a heavy storm.[10]
DK1/9: Completed 22 August 1993.[11]
DK1/20: Completed 13 August 1998.[12]
DK1/21: Completed 19 August 1998. This rig includes a lighthouse.[13]
^"Glossary of names - South China Sea". www.globalsecurity.org. Retrieved 6 June 2014.
^"Bombay Castle". East Asian Studies Library. Retrieved 6 June 2014.
^Pub 161 - Sailing Directions - South China Sea and the Gulf of Thailand (Ninth ed.). U.S.A: ProStar Publications, Inc. 20 November 2004. p. 14. ISBN 157785652X. Retrieved 6 June 2014.
^Samuels, Marwyn (2013). Contest for the South China Sea. Routledge. p. 191. ISBN 1136575537. Retrieved 6 June 2014.
^Valencia, Mark J.; Dyke, Jon M. Van; Ludwig, Noel A. (July 1999). Sharing the Resources of the South China Sea. University of Hawaii Press. ISBN 0824818814. Retrieved 6 June 2014.