Cornwall in the First World War

During this month, each weekday I'm posting a photograph showing Cornwall's First World War.

Here's an image from Fowey. By the riverside, soldiers guard a stack of boxes while an officer supervises. A small crowd of spectators has gathered and the town policeman stands by. 

But what is the photo showing us? Why have the army and constabulary turned out? And what do the boxes contain? Any information on this image would be gratefully received.

Update: Poltair History Department at https://twitter.com/HistoryPoltair and Fowey wooden boatbuilder Marcus Lewis at http://www.woodenboatbuilder.co.uk/ have come forward. They feel the boxes may contain ammunition for use on a rifle range across the water at Polruan. Many thanks for your help.

My book, 'Cornwall In The First World War', is published by Truran. With 112 pages and 100 images, you'll find it in bookshops across the Duchy. It's also available through Amazon: http://amzn.to/19JbtZm