In the 1950s he married, as her third husband, the celebrated wartime SOE heroine Odette. She had survived capture, torture in  Fresnes prison and incarceration in Ravensbrück concentration camp, and was awarded the George Cross.

Hallowes had served with the 2nd Battalion The Gordon Highlanders in the final stage of the unsuccessful struggle to establish a defence of Malaya against the Japanese offensive.

Despite the numerical superiority of General Percival's British, Australian, Indian and Malay troops, the Japanese prevailed. The 2nd Gordons and 2nd Argyll and Sutherland Highlanders were the last units to cross into  Singapore before the causeway was blown

When the island surrendered on February 15, 1942, he was one of four officers sent in pairs to carry the ceasefire order to the garrisons of the outlying islands of Balang Mati and Pulau Brani.

Their progress was slow, especially after  Nicholson's paddle snapped, but they found four British soldiers on a nearby island with a barely serviceable boat and two oars

After they had rowed for five days with loops of rope deputising for the missing rowlocks, the dinghy ran aground on a reef off the east coast of Sumatra and sank. Unaware that the Japanese had landed on the south west of the island, the six men followed a river bed and crossed the western range of hills to the small port of Padang on the west coast.

There they spent a week in a fruitless search for
another boat, but rescue came in the form of a Royal Navy destroyer calling to refuel, after having taken part in the Battle of the Java Sea. This took them to Ceylon (now Sri Lanka), from where they were flown to India.

On reaching Bombay in May 1942, Hallowes was employed as a staff captain dealing with administrative matters in the local headquarters. He escaped this by volunteering for the Special Operations Executive and attending the special forces training school at Haifa. He then joined the Yugoslav section of SOE's Force 133, based in Cairo.