**His first novel, “HMS Ulysses” is loosely based on PQ-17.**
I read that 51 years ago! Excellent book on the terrors of arctic warfare.
The ship is sunk, men are in the water crying for rescue! You get a Ping that an enemy sub is beneath you, you drop a depth charge hoping to nail the enemy sub, but you know the concussion will also kill the men in the water.
Hypothermia would probably have got them before anything could have been done, even without the threat of being torpedoed while stopping in an attempt to pick up survivors.
Besides, by that time, the then-secret hedgehog was in use. There's a reason that no war time movies used footage of it in action.