Bull Sand Fort under construction: main floor, 4 November 1917

This photograph is one of a rare collection of nine images preserved by the Trevitt Collection, documenting the construction of the Humber sea forts during the First World War. Eight photographs record the building of Bull Sand Fort, while a ninth shows work on Haile Sand Fort (described in some contemporary records as Sandhail Fort). Together they provide an exceptional visual record of one of Britain's greatest wartime engineering projects.

Dated 4 November 1917, as recorded on the original negative, this photograph shows Bull Sand Fort during the main phase of its construction. The massive circular concrete foundation is complete, while work continues on the structure within it. Several substantial steel grillages, which would support the fort's main structural stanchions, can be seen on the concrete floor. A small workboat rests beside them.

Men are at work on the surrounding structure, with timber staging, temporary walkways, ladders and construction materials covering the unfinished levels. The scale of the construction can be seen from the men working around the perimeter and the small boat resting on the main floor.

Construction of Bull Sand Fort began in 1915 as part of Britain's First World War coastal defence programme. Built by C. J. Wills & Sons Ltd. under the direction of Major-General Sir G. K. Scott-Moncrieff, the fort was designed to protect the approaches to the Humber and the strategically important ports of Hull, Grimsby and Immingham. Although considerable progress had been made when this photograph was taken, work continued until the fort was officially completed in December 1919.

Few contemporary photographs survive showing the Humber sea forts under construction. The Trevitt Collection therefore provides an important record of the engineers and workmen who built these remarkable offshore defences, which remain prominent landmarks at the mouth of the Humber today.

Photograph: The Trevitt Collection Date: 4 November 1917 Location: Bull Sand Fort, Humber Estuary