On her eighteenth birthday, Mavis enlisted in the WRNS. Less than a year later, in early 1944, she was selected to be assigned to Southwick House (HMS Dryad), north of Portsmouth, as one of only a dozen telephonists, operating the switchboard in the basement of what became the headquarters of the main Allied Commanders, including Allied Supreme Commander General Eisenhower, Naval Commander-in-Chief Admiral Ramsay and Army Commander-in-Chief General Montgomery.
She stayed in the WRNS until December 1944, then marrying her boyfriend, Bill Egerton, a paratrooper who had landed in Normandy in a Horsa glider on the evening of D-Day, two months before his eighteenth birthday. Married women, at that time, were usually demobbed. After WWII, she raised two daughters, worked in the commercial sector and later, for the Red Cross.