During World War II Mais served as a major with Special Forces in France, Iran and Iraq. After returning to Britain late in 1943, his orders were to develop the Mulberry harbour project for the D-Day landings.
When construction began off the Normandy coast immediately after D-day (6 June 1944) Mais, promoted lieutenant-colonel, was in charge of constructing the pierheads and floating roadways at the British harbour under ColonelStuart Gilbert of the Royal Engineers, who commanded the port construction force.
In 1936 Mais married Lorna Aline, daughter of Stanley Aspinall Boardman, wool merchant, of Addiscombe in Surrey, by whom he had two sons and a daughter.
Coat of arms of Alan Mais, Baron Mais
Crest
A demi-sea Horse per pale Argent and Gules finned Or the dexter Fin grasping a Sword Gules and resting the sinister upon an Anchor flukes to the sinister Sable.
Escutcheon
Per pale Argent and Gules a Chevron engrailed between in chief two Cinquefoils and in base a Rose all Counterchanged on a Chief Azure a Griffin passant Or supporting with the dexter Claw a paving Stone Argent.
Supporters
Dexter a Griffin, sinister a Dragon, both Gules armed and langued Azure winged Argent and gorged with a collar embattled Argent charged with a barrulet wavy Azure.