Britain's Ministry of Defence on Sunday defended its practice of shooting pigs and giving the wounded animals to military surgeons to practice treating common battlefield injuries.
Royal Society for the Prevention of Cruelty to Animals spokesperson Klare Kennett said the training exercises, which take place twice a year in Denmark, were "abhorrent and shocking".
"Pigs are intelligent animals and most people would be appalled by this, especially as there is an alternative available which does not involve harming any animals," she said.
The ministry said the training gave surgeons "invaluable experience" and "helped save lives on operations".
The animals are heavily anaesthetised before being shot at close range "to damage organs but not kill the animals", and are then operated on before being killed humanely, the ministry said.
"This training provides invaluable experience, exposing our surgical teams to the specific challenges posed by the injuries of modern armed conflict," a spokesperson said.
"This training has helped save lives on operations and by participating in the Danish exercises we minimise the overall number of animals used."
Animal rights campaigners argue that life-like human simulator devices are more effective for medical training than live animals.
But the courses, which were suspended in 1998, were reinstated after a government-commissioned study found that "no equally effective alternative" existed.