What mandatory equipment is required for SCUBA diving?

The requirement of a knife as mandatory equipment for SCUBA diving is critical for ensuring safety during dives. A dive knife serves multiple important purposes: it can be used to cut away entangled lines, fishing nets, or any other materials that may pose a risk of entrapment under water. Its portability and reliable accessibility at a diver's side can be life-saving in emergency situations where quick action is necessary.

While the other pieces of equipment listed—wetsuits, regulators, and snorkels—are indeed important for comfort and maneuverability or for specific diving situations, they do not fulfill as critical a safety role as a dive knife in emergency scenarios. Divers should be familiar with and ready to utilize a knife effectively before submerging to enhance their safety in potentially hazardous underwater environments.