Boat Troop were trained as commando frogmen. Some amphibious brigade personnel are trained as frogmen. In an incident on the coast of Nicaragua PDSS frogmen killed trained anti-frogman dolphins. Nets protected ships at anchor, especially as obstacles against submarines, human torpedoes, and frogmen. Maiale, used by Italy's Decima Flottiglia MAS, and Chariots, used by British commando frogmen. Sonar can be used to detect frogmen and other scuba divers. France further developed the role of commando frogmen in the First Indochina War. For other events, see Operations of X Flottiglia MAS and British commando frogmen. In Britain, police divers have often been called "police frogmen". Italy was the first nation to use frogmen and human torpedoes. The APS was the primary weapon of Soviet frogmen and Serbian river flotilla frogmen. A unit of naval frogmen to serve as suicide bombers, called the Fukuryu, was raised. Three Polish military units train and deploy frogmen in military operations. In 1974, a research team dealing with matters related to naval frogmen was created. The SEAL Museum stands on the training site of the first Navy frogmen.