[siber]

Never try to torpedo Passenger/Cargo ships when there are other targets about. Those things eat torpedoes for breakfast! Seriously, most ships sink after a single torpedo hit in anything but calm weather. Passenger/Cargo ships generally require 2 or more torpedos before sinking...

I think the Tommies use the Passenger/Cargo vessels to transport vital war supplies such as helium gas and ping-pong balls across the atlantic. They just do not want to sink!