Some 288 military dogs have been put down by the Ministry of Defence in the past three years.
The figures emerged after it was revealed that two guard dogs used to protect the Duke of Cambridge were euthanised within days of him leaving his military base.
According to the Sun, 288 dogs were put down by the MoD from January 2010 to June this year.
Among those humanely killed, 81 were because of age, 61 due to osteoarthritis and 33 were related to dangerous temperament.
An MoD spokesman said: "Our animals play an invaluable role on military operations in Afghanistan and elsewhere and are much loved by the troops.
"Most animals are re-homed. Regrettably, due to the challenging nature of their work, some of our dogs get injured or contract illnesses and need to be put down. These decisions are taken only as a last resort following veterinary advice."
The Sun reported that Bruce, a Belgian Shepherd, and Blade, a German Shepherd, were put down after William completed his final shift as a search and rescue pilot at RAF Valley on Anglesey.
In a further statement, the MoD added: "Our policy on military working dogs is clear - we make every effort to re-home all military working dogs at the end of their service life and hundreds have gone to those closely associated with the animal while it was serving, or to others within the military community.
"Regrettably, due to the nature of their work, some dogs can develop veterinary problems and it would be inappropriate and inhumane to re-home them. Putting a dog down is only ever taken as a last resort. Indeed, the MoD has a team of veterinary staff and local vet practices working at specialist facilities in the UK, Germany and Afghanistan to provide our dogs with the care they need around the clock.
"The vast majority of dogs put down over the past three years was based on a veterinary diagnosis which concluded that the animal's condition impeded their quality of life. In certain circumstances, the veterinarian judges that it is unsafe to re-home the animal because of the risk they pose to the public or where re-homing them would conflict with the animal's welfare."