Military animals can be used to assist with a range of tasks (Picture: US Air Force).
The link between the military and animals is a long and strong one.
For more than 50 years, dogs have been taught the skill of arms explosive detection.
Canines are trained for a range of specialisms, including protection, ensuring bases and military sites are kept secure, to detecting arms and explosives.
The value of the dogs to the military remains clear - each year the Royal Army Veterinary Corps trains up to 170 dogs every year, which go on to serve in the military and police force.
Meanwhile, horses, once a key part of battlefield tactics, continue to play a large role in a ceremonial capacity.
Mules are used by the German Army to navigate mountains with equipment loads, while the US Marines' Mountain Warfare Centre uses "horses and mules as a way of transporting people, weapons and equipment across high altitude complex compartmentalised terrain".
Even eagles have been trained in some nations to hunt drones.
Dolphins are used by some countries - the United States, Russia, Iran and Ukraine are among those known to use the highly intelligent mammals.
The US Navy uses bottlenose dolphins in tandem with sea lions, as part of its Marine Mammal Programme.
The Defence Secretary Gavin Williamson is a conservationist and lover of animals.
So how have militaries from across the world have been celebrating this day?