Felixstowe Flying-boat under tow in the N Sea

Felixstowe flying-boat being towed at high speed by a destroyer in the North Sea, 1918/19.
Another is visible in the background.

There are three similar photos, the handwritten captions on the backs of the original prints read:
"Flying Boat being towed in North Sea at 21 knots on a lighter. Stern of Destroyer shewing. This I understand is one of the worst stunts you can be on."
"Another of the same. Depth charge for submarines."
"Another of the same only closer view. Note the wash, which makes it pleasant for those on lighter."