Collingwood Ingram set off across the Channel to St-Omer in northern France on 7 December 1916. He spent the next two years with the Royal Flying Corps, servicing the compasses on the planes and, in his off-duty hours, continuing research for his planned book on the birds of France.

His diaries record both his experiences of the war and the birds. He flew with the pilots whenever he got the chance, made friends with them and mourned the loss of many, but he did not neglect to ask them what birds they had seen when flying, and how high they flew.

A particular friend was Eric Lubbock, son of Sir John Lubbock, eminent scientist and friend of Darwin. In the short time Collingwood knew Eric Lubbock, he came to admire, almost revere, him. When Collingwood's first and only daughter was born on 4 January 1917, Eric Lubbock was her godfather. When he was killed only a few weeks later, Collingwood wrote of him in his diary,

'There have been few finer characters than Lubbock – a man of more than ordinary intelligence, he devoted all his mental and physical energy to his work and during my stay with 45 Squadron no pilot was so frequently in air. Absolutely unaffected, he was as courteous as he was kind, and from the very first moment I saw him he treated me with a natural politeness that set me entirely at my ease and made me feel as though I had known him for years. This sincerity was unquestionable. With Lubbock’s death the Flying Corps has lost a valuable officer and England a gallant pure-minded gentleman that will be difficult to replace.'