Complex sentence: He then joined the infantry of the Canadian Army in 1915; however, he requested a transfer and returned from overseas to take flying lessons at his own expense at the Curtiss Aviation School at Toronto, Ontario, graduating on August 11,1916.
Split into simpler sentences: He then joined the infantry of the Canadian Army in 1915. He requested transfer and returned from overseas to take flying lessons at his own expense at the Curtiss Aviation School at Toronto, Ontario, graduating on August 11,1916.