Why German battleships demanded close attention

Why was Britain so concerned about German battleships during the Second World War?

Because earlier German raids had strong political effects and a single battleship loose among a convoy could cause catastrophic losses.

The Royal Navy itself was not simply terrified, although political leaders were deeply anxious. German battlecruiser raids against the British coast during the First World War shaped that fear. In the Second World War, the operational problem was straightforward: even one German battleship breaking into a convoy could destroy merchant ships faster than escorts could respond, so the threat had to be watched and contained.