The two trophy guns are Dahlgren guns, not Parrotts. You can tell by the "soda bottle" shape.

The contemporary photo below shows the Derryfield Park cannon at ground level, while the historic view shows a similar Dahlgren in a Civil War battery.

Parrott rifles, very serious artillery in Civil War days.

Those mill buildings are still there, converted into upscale commercial space. And the dam generates hydro power. I travel through Manchester every time I head to the White Mountains to ski or hike.

Given the line of mills in the background there, my guess is this view is looking east over Manchester towards the Merrimack River. Google Earth shows the two cannons still seem to be there.

A virtual drive around Manchester reveals all of these stacks are gone. In England most of the mills have been converted to upperclass appartments due to high ceilings and generous windows . They sometimes leave the stack standing. This photograph must have been taken near the McIntyre Ski lifts . The photo was taken looking SW toward the Merrimac river which runs almost NS for awhile . The rows of warehouses in the lower mid to right on this side of the river are still there . As is Ste Marie , the prominent church behind them on the other side of the river.

Visible to the right of Oak Hill Reservoir in this aerial view.