The son of W. A. Erwin of Chicago, Illinois, William Portwood Erwin was assigned to the 1st Observation Squadron on 19 July 1918. A Salmson 2A2 pilot, he and his observers were credited with 8 victories. He and his navigator, Alvin H.Eichwaldt, were lost at sea while searching for two planes, the Golden Eagle and the Miss Doran, that were missing in the Pacific during the Dole Air Race from California to Hawaii in 1927.
The Distinguished Service Cross is presented to William P. Erwin, First Lieutenant (Air Service), U.S. Army, for extraordinary heroism in action in the Chateau-Thierry and St. Mihiel Salients, France. Lieutenant Erwin, with Second Lieutenant Byrne E. Baucom, observer, by a long period of faithful and heroic operations, set an inspiring example of courage and devotion to duty to his entire squadron. Throughout the Chateau- Thierry actions, in June and July, 1918, he flew under the worst weather conditions and successfully carried out his missions in the face of heavy odds. In the St. Mihiel sector, September 12 - 15, 1918, he repeated his previous courageous work. He flew as low as 50 feet from the ground behind the enemy's lines, harassing German troops with machine-gun fire and subjecting himself to attack from ground batteries, machine- guns, and rifles. He twice drove off enemy planes which were attempting to destroy an American observation balloon. On September 12 and 13, 1918, he flew at extremely low altitudes and carried out infantry contact patrols successfully. Again on September 12 he attacked a German battery, forced the crew to abandon it, shot off of his horse a German officer who was trying to escape, drove the cannoneers to their dugouts, and kept them there until the infantry could come up and capture them.
General Orders No. 70, W.D., 1919
French Croix de Guerre
On 20 July 1918, he volunteered for an infantry liaison mission at night fall, executed this mission at 200 meters altitude. He brought back his observer, who was mortally wounded, and his plane was full of bullet holes.