Simon was born in 1947 in Hong Kong. As a half-grown cat, he was taken aboard the HMS Amethyst to control rats. In 1949, the ship was attacked on the Yangtze River in China by communists. Simon was wounded, but not found for days. The injured sailors had been evacuated, so the ship's doctor nursed Simon's facial burns and shrapnel wounds. As Simon recovered he resumed rat catching, but also added the duty of visiting sick and wounded sailors.
Upon his return to Hong Kong, Simon was presented with a campaign ribbon and news that he would receive a Dicken Medal, an award for animal gallantry. When the Amethyst reached England, Simon had to go into quarantine. He developed an infection and died just before his planned formal medal ceremony. The veterinarian believed the young cat would have recovered if his war wounds hadn't weakened him. Simon was buried in a specially-made casket with full naval honors.