The years that followed the end of hostilities were scarcely less adventurous for him, for between 1920 and 1924 he was British liaison officer with the French in Syria and participated with a pioneering journey across the Syrian Desert in 1923.

A party consisting of McCallum, Mr. Palmer, Consul in Damascus, Mahommed Ibn Bassam, a gold trader, drove from Syria to Baghdad in three cars, a Buick, an Oldsmobile, and a Lancia.

The party entrained at Bangkok, entered Malaya through Kedah, traveling south to Singapore, there taking ship to Rangoon and thence by sea to Calcutta, after spending a week trying to find an overland route into Burma.

After reaching Calcutta they drove across India by way of Lahore, Peshawar, and Quetta, across the Balochistan desert, through north-eastern Persia to Meshed; thence to Teheran, Baghdad, Damascus, and Beirut.

The journey from Constantinople (Istanbul) was through Bulgaria at the time an earthquake occurred, and the party arrived from Adrianople at the village of Papazali the day after it had been laid in ruins.