A Bridge of Magpies — Geoffrey Jenkins

The U - boat veered. This was the moment I'd been waitng for. I dived. The icy water was a terrible shock. I went down, down, down. Then the U - boat's black shadow came between me and the surface, the hulk trailing weed and rust. As I kicked myself upwards my hands touched something smooth and round, with a small propeller sticking out from it. I shot to the surface, gasping from fear and lack of air. Denny was coming towards me in the Gaok. I yelled, "keep away! There's a half fired torpedo under her..."

"A superior thriller"
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