The fortress was built around 1902 as a coastal defence against enemy vessels on the west side of the Isle of Portland. The fort was re-equipped during both World Wars, including 9.2 inch guns during the First World War. During World War 2, on the night of the 27 April 1944, the fort witnessed the Slapton Sands Massacre. When German E-Boats attacked landing crafts carrying United States soldiers, on exercise in Lyme Bay, the fort's gunners were ordered not to open fire for fear of causing friendly casualties. More than 600 American soldiers and seamen drowned by the end of the night, many were pulled down by the weight of their own equipment.
- "Quick facts about the Jurassic Coast". Jurassiccoastline.com. 1944-04-27. Retrieved 2012-09-27.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
- "Blacknor, Portland, Dorset". Geoffkirby.co.uk. Retrieved 2012-09-27.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
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