Geoffersincornwall,
I have trouble with the idea that weaving the ship will help it at all, unless U-Boats are still out there with dumb, unguided torpedos. Modern subs with wire guided and automatic tracking torpedos, as well as various missiles that could care a fig if that 20 knot pile of steel (known by its nick-name, "Target") is weaving about.
Sounds like the British Navy has the same type of fellows that CAA does when they make you memorize Morse Code!
If naval ships still weave, it is probably to drive off those pesky helicopters!