Explanation:

- Option 1: Bombs that could destroy submarines is correct. Hedgehogs were a type of anti-submarine weapon used during World War II. They launched multiple small spigot bombs in a pattern that increased the chances of hitting a submarine.

- Option 2: Special radar installations do not describe hedgehogs, which were a type of weapon, not radar.

- Option 3: Machines that could decode German secret messages, like the Enigma machine, were not referred to as hedgehogs.

- Option 4: Small ships that could chase down submarines do not describe hedgehogs, which were deployed from larger ships.