Losses of British warships were small. Although the battleship "Formidable" had been sunk by "U-24" on New Year's Day, the fast destroyer screens soon made successful attacks on battleships and cruisers a thing of the past. On the other hand, there was little a Royal Navy warship could do to sink a U-boat if the submarine's captain was reasonably alert. The U-boat was generally safe from shelling once it had submerged. It could be rammed if it were at periscope depth, but ramming was hardly a reasonable tactic as a standard practice.